Open Source AsyncDNS.*, DNS.* and DnsProbe.* histograms.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index e8356b5a59e123532b38c0abc94d715ab35a0280..5f544d49a4c1fecd3a7857f504eaf5806d771aa6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -55,6 +55,358 @@ other types of suffix sets.
 
 <histograms>
 
+<histogram name="AsyncDNS.ConfigChange" enum="BooleanSuccess">
+  <summary>
+    Whether DnsConfigService::OnConfigChange actually corresponded to a change
+    in DnsConfig.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ConfigNotifyInterval" units="milliseconds">
+  <summary>
+    Duration of time between calls to DnsConfigService::InvalidateConfig.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ConfigParseDuration" units="milliseconds">
+  <summary>Duration of time spent parsing DnsConfig.</summary>
+</histogram>
+
+<histogram name="AsyncDNS.ConfigParsePosix" enum="AsyncDNSConfigParsePosix">
+  <summary>
+    Counts of results of parsing DnsConfig in DnsConfigServicePosix.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ConfigParseResult" enum="BooleanSuccess">
+  <summary>Whether DnsConfig was parsed successfully.</summary>
+</histogram>
+
+<histogram name="AsyncDNS.ConfigParseWin" enum="AsyncDNSConfigParseWin">
+  <summary>
+    Counts of results of parsing DnsConfig in DnsConfigServiceWin.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.DNSChangerDetected" enum="BooleanSuccess">
+  <summary>
+    Whether the first valid DnsConfig included a rogue nameserver.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.DnsClientDisabledReason" enum="NetErrorCodes">
+  <summary>
+    Counts of specific error codes returned by DnsTask if a subsequent ProcTask
+    succeeded, at the end of a streak of failures after which the DnsClient was
+    disabled.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.DnsClientEnabled" enum="BooleanSuccess">
+  <summary>
+    TRUE counts the events when a valid DnsConfig is received and used to enable
+    DnsClient, while FALSE counts the events when DnsClient is disabled after a
+    series of successful fallbacks from DnsTask to ProcTask.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.FallbackFail" units="milliseconds">
+  <summary>
+    Duration of time spent by ProcTask in failing fallback resolutions.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.FallbackSuccess" units="milliseconds">
+  <summary>
+    Duration of time spent by ProcTask in successful fallback resolutions.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.HaveDnsConfig" enum="BooleanSuccess">
+  <summary>
+    Whether there was a valid DNS configuration at the start of a job which
+    eventually completed successfully.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.HostParseResult" enum="BooleanSuccess">
+  <summary>Whether DnsHosts were parsed successfully.</summary>
+</histogram>
+
+<histogram name="AsyncDNS.HostsChange" enum="BooleanSuccess">
+  <summary>
+    Whether DnsConfigService::OnHostsChange actually corresponded to a change in
+    DnsHosts.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.HostsNotifyInterval" units="milliseconds">
+  <summary>
+    Duration of time between calls to DnsConfigService::InvalidateHosts.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.HostsParseDuration" units="milliseconds">
+  <summary>Duration of time spent parsing DnsHosts.</summary>
+</histogram>
+
+<histogram name="AsyncDNS.HostsParseWin" enum="AsyncDNSHostsParseWin">
+  <summary>
+    Counts of results of parsing DnsHosts in DnsConfigServiceWin.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.HostsSize" units="bytes">
+  <summary>
+    The size of the HOSTS file observed before each attempt to parse it.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTime" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (using DnsClient).
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTime_HIGHEST" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (using DnsClient). Includes only Jobs which had
+    priority HIGHEST when started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTime_IDLE" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (using DnsClient). Includes only Jobs which had
+    priority IDLE when started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTime_LOW" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (using DnsClient). Includes only Jobs which had
+    priority LOW when started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTime_LOWEST" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (using DnsClient). Includes only Jobs which had
+    priority LOWEST when started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTime_MEDIUM" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (using DnsClient). Includes only Jobs which had
+    priority MEDIUM when started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTimeAfterChange" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (using DnsClient).
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTimeAfterChange_HIGHEST" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (using DnsClient). Includes only Jobs which had priority HIGHEST
+    when started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTimeAfterChange_IDLE" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (using DnsClient). Includes only Jobs which had priority IDLE when
+    started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTimeAfterChange_LOW" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (using DnsClient). Includes only Jobs which had priority LOW when
+    started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTimeAfterChange_LOWEST" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (using DnsClient). Includes only Jobs which had priority LOWEST when
+    started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.JobQueueTimeAfterChange_MEDIUM" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (using DnsClient). Includes only Jobs which had priority MEDIUM when
+    started.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ParseToAddressList" enum="AsyncDNSParseResult">
+  <summary>
+    Counts of results of parsing addresses out of DNS responses in successful
+    DnsTransactions.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ResolveError" enum="NetErrorCodes">
+  <summary>
+    Counts of specific error codes returned by DnsTask if a subsequent ProcTask
+    succeeded.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ResolveFail" units="milliseconds">
+  <summary>
+    Duration of time taken by DnsTask in resolutions that failed. Excludes time
+    spent in the subsequent fallback.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ResolveStatus" enum="AsyncDNSResolveStatus">
+  <summary>
+    Counts of the overall results of using asynchronous DNS in HostResolverImpl.
+    This only includes jobs started with valid DNS configuration and excludes
+    synchronous resolutions (as IP literals, from cache, and from HOSTS).
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ResolveSuccess" units="milliseconds">
+  <summary>
+    Duration of time taken by DnsTask in resolutions that succeeded.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ResolveSuccess_FAMILY_IPV4" units="milliseconds">
+  <summary>
+    Same as AsyncDNS.ResolveSuccess, but limited to pure IPv4 lookups.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ResolveSuccess_FAMILY_IPV6" units="milliseconds">
+  <summary>
+    Same as AsyncDNS.ResolveSuccess, but limited to pure IPv6 lookups.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.ResolveSuccess_FAMILY_UNSPEC" units="milliseconds">
+  <summary>
+    Same as AsyncDNS.ResolveSuccess, but limited to IPv4/IPv6 lookups.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.SortFailure" units="milliseconds">
+  <summary>
+    Duration of time taken in failing calls to AddressSorter in dual-stack
+    resolutions using DnsTask.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.SortSuccess" units="milliseconds">
+  <summary>
+    Duration of time taken in successful calls to AddressSorter in dual-stack
+    resolutions using DnsTask.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.TotalTime" units="milliseconds">
+  <summary>
+    Duration of time since a HostResolverImpl::Resolve request to the time a
+    result is posted. Excludes canceled, evicted, and aborted requests. Includes
+    cache hits (recorded as 0). Excludes speculative requests.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.TotalTime_speculative" units="milliseconds">
+  <summary>
+    Duration of time since a HostResolverImpl::Resolve request to the time a
+    result is posted. Excludes canceled, evicted, and aborted requests. Includes
+    cache hits (recorded as 0). Speculative requests only.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.TransactionFailure" units="milliseconds">
+  <summary>
+    Duration of time taken in failing DnsTransactions. This includes server
+    failures, timeouts and NXDOMAIN results.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.TransactionSuccess" units="milliseconds">
+  <summary>
+    Duration of time taken in successful DnsTransactions. This includes all
+    NOERROR answers, even if they indicate the name has no addresses or they
+    cannot be parsed.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.TransactionSuccess_A" units="milliseconds">
+  <summary>
+    Same as AsyncDNS.TransactionSuccess but limited to A query type.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.TransactionSuccess_AAAA" units="milliseconds">
+  <summary>
+    Same as AsyncDNS.TransactionSuccess but limited to AAAA query type.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.TTL" units="milliseconds">
+  <summary>
+    TTL of the resolved addresses, as in the response received from the server.
+    For results served from local cache, the TTL is from the original response.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.UDPAttemptFail" units="milliseconds">
+  <summary>
+    Duration of time taken by DnsUDPAttempt in failed attempts. Excludes
+    timeouts.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.UDPAttemptSuccess" units="milliseconds">
+  <summary>
+    Duration of time taken by DnsUDPAttempt in successful attempts. Includes
+    responses arriving after timeout, if multiple attempts are allowed.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.UnchangedConfigInterval" units="milliseconds">
+  <summary>
+    Duration of time since the last empty config result to the time a non-change
+    OnConfigChange is received.
+  </summary>
+</histogram>
+
+<histogram name="AsyncDNS.UnchangedHostsInterval" units="milliseconds">
+  <summary>
+    Duration of time since the last empty config result to the time a non-change
+    OnHostsChange is received.
+  </summary>
+</histogram>
+
 <histogram name="Autocheckout.Bubble" enum="AutocheckoutBubble">
   <summary>
     Measures the frequency of user interactions with the Autocheckout bubble,
@@ -494,6 +846,545 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="DNS.AttemptCancelled">
+  <summary>
+    The attempt which completed after the job was already cancelled.
+  </summary>
+</histogram>
+
+<histogram name="DNS.AttemptDiscarded">
+  <summary>
+    The attempt which completed after the job was already cancelled OR the
+    attempt that has finished after host resolution was already completed by an
+    earlier attempt.
+  </summary>
+</histogram>
+
+<histogram name="DNS.AttemptFailDuration" units="milliseconds">
+  <summary>
+    Duration of time taken in OS resolutions for actual navigations. These
+    attempts which completed after the job was already canceled OR after the job
+    was already completed by an earlier attempt. Note that cached resolutions
+    may provide low (0ms?) resolution times.
+  </summary>
+</histogram>
+
+<histogram name="DNS.AttemptFailure">
+  <summary>The attempt that has not resolved the host successfully.</summary>
+</histogram>
+
+<histogram name="DNS.AttemptFirstFailure">
+  <summary>
+    The attempt that resolved the host first and the resolution was not
+    successful.
+  </summary>
+</histogram>
+
+<histogram name="DNS.AttemptFirstSuccess">
+  <summary>
+    The attempt that resolved the host first and the resolution was successful.
+  </summary>
+</histogram>
+
+<histogram name="DNS.AttemptSuccess">
+  <summary>The attempt that has resolved the host successfully.</summary>
+</histogram>
+
+<histogram name="DNS.AttemptSuccessDuration" units="milliseconds">
+  <summary>
+    Duration of time taken in OS resolutions that succeeded and were requested
+    for actual navigations. These attempts which completed after the job was
+    already canceled OR after the job was already completed by an earlier
+    attempt. Note that cached resolutions may provide low (0ms?) resolution
+    times.
+  </summary>
+</histogram>
+
+<histogram name="DNS.AttemptTimeSavedByRetry" units="milliseconds">
+  <summary>
+    This histogram shows the time saved by having spawned an extra attempt, when
+    the first attempt didn't finish before retry attempt.
+  </summary>
+</histogram>
+
+<histogram name="DNS.CacheEvicted" units="milliseconds">
+  <summary>
+    The time left to expiration of an entry when it is removed while compacting
+    the HostCache.
+  </summary>
+</histogram>
+
+<histogram name="DNS.CacheExpired" units="milliseconds">
+  <summary>
+    The time since expiration of an entry when it is removed while compacting
+    the HostCache.
+  </summary>
+</histogram>
+
+<histogram name="DNS.CacheExpiredOnGet" units="milliseconds">
+  <summary>
+    The time since expiration of an entry when it is removed on lookup.
+  </summary>
+</histogram>
+
+<histogram name="DNS.EmptyAddressListAndNoError">
+  <summary>

[mef, 2013/05/13 21:20:11]

Jim, 

thank you for your suggestion on another CL. In retrospect, we could've added
this count as a bucket to another histogram, probably ResolutionCategory enum.
The idea here is to try to explicitly record scenarios where AsyncDNS reports
failure, but ProcDNS succeeds, and this appears to be one of the plausible
explanations.

+    Host Resolver OnLookupComplete got empty address list, and no error.
+  </summary>
+</histogram>
+
+<histogram name="DNS.IndependentFailedNavigation" units="milliseconds">
+  <summary>
+    When either a pre-resolution was not done recently enough to provide
+    benefit, or the the corresponding pre-resolution is still pending, this
+    histogram shows the duration of time used to resolve a hostname as not
+    existing during a failed attempt to navigate to (GET) a URL.  In newer
+    versions, if the hostname has never been found as a link during a page scan,
+    and it has a referring URL, then it is added to referrer list data structure
+    (hoping we'll do better next time).
+  </summary>
+</histogram>
+
+<histogram name="DNS.IndependentNavigation" units="milliseconds">
+  <summary>
+    When either a pre-resolution was not done recently enough to provide
+    benefit, or the the corresponding pre-resolution is still pending, this
+    histogram shows the duration of the duration of time used to resolve a
+    hostname to navigate to (GET) a URL.  In newer versions, if the hostname has
+    never been found as a link during a page scan, and it has a referring URL,
+    then it is added to referrer list data structure (hoping we'll do better
+    next time).
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTime" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (a getaddrinfo call was dispatched to the thread
+    pool).
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTime_HIGHEST" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (a getaddrinfo call was dispatched to the thread
+    pool). Includes only Jobs which had priority HIGHEST when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTime_IDLE" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (a getaddrinfo call was dispatched to the thread
+    pool). Includes only Jobs which had priority IDLE when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTime_LOW" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (a getaddrinfo call was dispatched to the thread
+    pool). Includes only Jobs which had priority LOW when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTime_LOWEST" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (a getaddrinfo call was dispatched to the thread
+    pool). Includes only Jobs which had priority LOWEST when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTime_MEDIUM" units="milliseconds">
+  <summary>
+    Time elapsed between the time the HostResolverImpl::Job was created and the
+    time the Job was started (a getaddrinfo call was dispatched to the thread
+    pool). Includes only Jobs which had priority MEDIUM when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTimeAfterChange" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (a getaddrinfo call was dispatched to the thread pool).
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTimeAfterChange_HIGHEST" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (a getaddrinfo call was dispatched to the thread pool). Includes
+    only Jobs which had priority HIGHEST when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTimeAfterChange_IDLE" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (a getaddrinfo call was dispatched to the thread pool). Includes
+    only Jobs which had priority IDLE when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTimeAfterChange_LOW" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (a getaddrinfo call was dispatched to the thread pool). Includes
+    only Jobs which had priority LOW when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTimeAfterChange_LOWEST" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (a getaddrinfo call was dispatched to the thread pool). Includes
+    only Jobs which had priority LOWEST when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.JobQueueTimeAfterChange_MEDIUM" units="milliseconds">
+  <summary>
+    Time elapsed between the last time the priority of a HostResolverImpl::Job
+    changed (when a Request was attached or detached) and the time the Job was
+    started (a getaddrinfo call was dispatched to the thread pool). Includes
+    only Jobs which had priority MEDIUM when started.
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchCacheEviction" units="milliseconds">
+  <summary>
+    The duration of time used (most recently) to pre-resolve a hostname, when
+    the prefetched resolution was apparently evicted from the cache.  The
+    included samples only list pre-resolution times when the later
+    navigations/fetches took in excess of 15ms.
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchCacheEvictionL" units="milliseconds">
+  <summary>
+    The duration of time used (most recently) to pre-resolve a hostname, when
+    the prefetched resolution was apparently evicted from the cache.  The
+    included samples only list pre-resolution times when the later
+    navigations/fetches took in excess of 15ms.
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchFoundName">
+  <summary>Replaced by DNS.PrefetchFoundNameL.</summary>
+</histogram>
+
+<histogram name="DNS.PrefetchFoundNameL" units="milliseconds">
+  <obsolete>
+    Deprecated 2/2010, and replaced by DNS.PrefetchResolution
+  </obsolete>
+  <summary>
+    The duration of time used by the DNS pre-resolving threads to resolve a host
+    name via the network.  Any resolutions that are faster than 15ms are
+    considered to be local cache hits, not requiring network access, and are not
+    included in this histogram. This histogram is most useful for estimating the
+    typical cost of a name resolution, but it also estimates the total number of
+    network-based resolutions induced by this feature.  Not all these
+    resolutions prove helpful (i.e., the user does not always actually visit the
+    resolved hostnames).
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchNegativeHit">
+  <summary>Replaced by DNS.PrefetchNegativeHitL.</summary>
+</histogram>
+
+<histogram name="DNS.PrefetchNegativeHitL" units="milliseconds">
+  <summary>
+    The duration of time saved due to DNS pre-resolving in the &quot;name not
+    found&quot; case.  Time &quot;savings&quot; shown in the histogram are
+    defined to be the difference between the DNS pre-resolution duration, and
+    the DNS resolution duration seen during a navigation.  These cache hits only
+    list events where the DNS pre-resolve duration for a host was in excess of
+    15ms (i.e., the network was consulted), and the actual DNS resolution (when
+    a user attempted to navigate to a link with the same host name) took less
+    than 15ms (i.e., the network was not consulted), which means the gain was a
+    result of a &quot;cache hit&quot; in the OS cache.  For some users with
+    LANs, all negative results (even when the DNS cache might otherwise help)
+    take about 2.5 seconds (due to timeouts for netbios broadcasts), and hence
+    no savings are possible (or shown) for such users in this category.
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchPositiveHit">
+  <summary>Replaced by DNS.PrefetchPositiveHitL.</summary>
+</histogram>
+
+<histogram name="DNS.PrefetchPositiveHitL" units="milliseconds">
+  <summary>
+    The duration of time saved due to DNS pre-resolving in the &quot;name was
+    found&quot; case, and induced by either a page scan for a link or an omnibox
+    entry by the user. Time &quot;savings&quot; shown in the histogram are
+    defined to be the difference between the DNS pre-resolution duration, and
+    the DNS resolution duration seen during a navigation.  These cache hits only
+    list events where the DNS pre-resolve duration for a host was in excess of
+    15ms (i.e., the network was consulted), and the actual DNS resolution (when
+    a user attempted to navigate to a link with the same host name) took less
+    than 15ms (i.e., the network was not consulted), which means the gain was a
+    result of a &quot;cache hit&quot; in the OS cache.
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchQueue" units="milliseconds">
+  <summary>
+    The duration of time spent by a proposed resolution waiting in the queue to
+    be resolved.  This number is in addition to any DNS resolution time that may
+    come later.
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchReferredPositiveHit" units="milliseconds">
+  <summary>
+    The duration of time saved due to DNS pre-resolving in the &quot;name was
+    found&quot; case, and induced by predicting (using referrer lists) that a
+    resolution was needed. Time &quot;savings&quot; shown in the histogram are
+    defined to be the difference between the DNS pre-resolution duration, and
+    the DNS resolution duration seen during a navigation.  These cache hits only
+    list events where the DNS pre-resolve duration for a host was in excess of
+    15ms (i.e., the network was consulted), and the actual DNS resolution (when
+    a user attempted to navigate to a link with the same host name) took less
+    than 15ms (i.e., the network was not consulted), which means the gain was a
+    result of a &quot;cache hit&quot; in the OS cache.
+  </summary>
+</histogram>
+
+<histogram name="DNS.PrefetchResolution" units="milliseconds">
+  <summary>
+    The duration of time used by the DNS pre-resolving threads to resolve a host
+    name via the network.  Any resolutions that are faster than 15ms are
+    considered to be local cache hits, not requiring network access, and are not
+    included in this histogram. This histogram is most useful for estimating the
+    typical cost of a name resolution, but it also estimates the total number of
+    network-based resolutions induced by this feature.  Not all these
+    resolutions prove helpful (i.e., the user does not always actually visit the
+    resolved hostnames).
+  </summary>
+</histogram>
+
+<histogram name="DNS.QueueRecycledDeltaOver2">
+  <summary>
+    When, due to congestion avoidance, a queued pre-resolution is abandoned
+    (recycled) without actually being resolved, this histograms records the age
+    in the queue of that entry.  Only times over 2 seconds are recorded in this
+    histogram.
+  </summary>
+</histogram>
+
+<histogram name="DNS.QueueRecycledUnder2">
+  <summary>
+    When, due to congestion avoidance, a queued pre-resolution is abandoned
+    (recycled) without actually being resolved, this histograms records the age
+    in the queue of that entry.  Only times less than or equal to 2 seconds are
+    recorded in this histogram.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveCategory" enum="ResolutionCategory">
+  <summary>
+    Counts of successes and failures of OS resolutions in various categories.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveFail" units="milliseconds">
+  <summary>
+    Duration of time taken in OS resolutions for actual navigations.  Note that
+    cached OS resolutions may provide low (0ms?) resolution times.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveFail_FAMILY_IPV4" units="milliseconds">
+  <summary>Same as DNS.ResolveFail, but limited to pure IPv4 lookups.</summary>
+</histogram>
+
+<histogram name="DNS.ResolveFail_FAMILY_IPV6" units="milliseconds">
+  <summary>Same as DNS.ResolveFail, but limited to pure IPv6 lookups.</summary>
+</histogram>
+
+<histogram name="DNS.ResolveFail_FAMILY_UNSPEC" units="milliseconds">
+  <summary>Same as DNS.ResolveFail, but limited to IPv4/IPv6 lookups.</summary>
+</histogram>
+
+<histogram name="DNS.ResolveSpeculativeFail" units="milliseconds">
+  <summary>
+    Duration of time taken in speculative OS resolutions.  Note that cached OS
+    resolutions may provide low (0ms?) resolution times.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveSpeculativeSuccess" units="milliseconds">
+  <summary>
+    Duration of time taken in speculative OS resolution that succeeded.  Note
+    that cached resolutions may provide low (0ms?) resolution times.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveSuccess" units="milliseconds">
+  <summary>
+    Duration of time taken in OS resolutions that succeeded and were requested
+    for actual navigations.  Note that cached resolutions may provide low (0ms?)
+    resolution times.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveSuccess_FAMILY_IPV4" units="milliseconds">
+  <summary>
+    Same as DNS.ResolveSuccess, but limited to pure IPv4 lookups.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveSuccess_FAMILY_IPV6" units="milliseconds">
+  <summary>
+    Same as DNS.ResolveSuccess, but limited to pure IPv6 lookups.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveSuccess_FAMILY_UNSPEC" units="milliseconds">
+  <summary>
+    Same as DNS.ResolveSuccess, but limited to IPv4/IPv6 lookups.
+  </summary>
+</histogram>
+
+<histogram name="DNS.ResolveUnspecWaste" enum="ResolutionUnspecWasteCategory">

[szym, 2013/05/13 19:19:26]

This histogram is gone. The enum is no longer needed.

[mef, 2013/05/13 21:20:11]

Done.

+  <summary>
+    Counts of hits and misses in the DNS cache and DNS jobs pool of wasted
+    HostResolverImpl::Jobs that could be avoided by always resolving using
+    AF_UNSPEC.
+  </summary>
+</histogram>
+
+<histogram name="DNS.TotalTime" units="milliseconds">
+  <summary>
+    Duration of time since a HostResolverImpl::Resolve request to the time a
+    result is posted. Excludes canceled, evicted, and aborted requests. Includes
+    cache hits (recorded as 0). Excludes speculative requests.
+  </summary>
+</histogram>
+
+<histogram name="DNS.TotalTime_speculative" units="milliseconds">
+  <summary>
+    Duration of time since a HostResolverImpl::Resolve request to the time a
+    result is posted. Excludes canceled, evicted, and aborted requests. Includes
+    cache hits (recorded as 0). Speculative requests only.
+  </summary>
+</histogram>
+
+<histogram name="DNS.UnexpectedResolution">
+  <summary>
+    In some cases, such as when content arrives with embedded references to
+    other servers, the prefetch system can't (or doesn't) attempt to pre-resolve
+    the hostnames.  As an example, a visit to www.cnn.com will fetch content
+    with references to about 12 additional hostnames, none of which are
+    currently anticipated.  Such resolutions are termed &quot;Unexpected
+    Resolutions,&quot; and the durations associated with those DNS resolutions
+    are shown below.  Future features may attempt to learn (from prior
+    experience locally, or from server provided hints), what secondary hostname
+    resolutions should be done when a primary resolution (or navigation) takes
+    place.  This histogram shows what the potential savings are that
+    &quot;remain on the table&quot; until we employ some of these more advanced
+    features.
+  </summary>
+</histogram>
+
+<histogram name="DNS.UnexpectedResolutionL">
+  <summary>
+    In some cases, such as when content arrives with embedded references to
+    other servers, or when a page (such as one in SSL) preclude scanning and
+    prefetching, the prefetch system can't (or doesn't) attempt to pre-resolve
+    the hostnames.  As an example, a visit to www.cnn.com will fetch content
+    with references to about 12 additional hostnames, none of which might be
+    anticipated.  Similarly, clicking on a link in an SSL page won't be
+    anticipated (since scanning in not allowed by default). Such resolutions are
+    termed &quot;Unexpected Resolutions,&quot; and the durations associated with
+    those navigation induced DNS resolutions are shown below.  If a referring
+    URL is available for the navigation, the relationship to the referring URL
+    was recorded, and future navigations to the referring hostname would have
+    induced a pre-resolution of hostname that caused an entry below.  Such any
+    entry may facilitate future listing in the ReferredPositiveHit histogram.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.Elapsed" units="ms">
+  <summary>Time between starting and finishing DNS probe.</summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.NcnOffline.Elapsed" units="ms">
+  <summary>
+    Time between starting and finishing DNS probe when NCN says we're offline.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.NcnOffline.Result" enum="DnsProbe.Probe.Result">
+  <summary>
+    Result of DNS probes sent by the probe service when NCN says we're offline.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.NcnOnline.Elapsed" units="ms">
+  <summary>
+    Time between starting and finishing DNS probe when NCN says we're online.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.NcnOnline.Result" enum="DnsProbe.Probe.Result">
+  <summary>
+    Result of DNS probes sent by the probe service when NCN says we're online.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.Result" enum="DnsProbe.Probe.Result">
+  <summary>Result of DNS probes sent by the probe service.</summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.ResultBadConfig.Elapsed" units="ms">
+  <summary>Elapsed time of DNS probes that return PROBE_BAD_CONFIG.</summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.ResultBadConfig.SystemIsLocalhost"
+    enum="DnsProbe.Probe.SystemIsLocalhost">
+  <summary>
+    Whether the only nameserver in the system DNS config was 127.0.0.1 when the
+    probe result was BAD_CONFIG.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.ResultBadConfig.SystemJobResult"
+    enum="DnsProbe.Job.Result">
+  <summary>
+    The result of the system probe job when the overall probe result was
+    BAD_CONFIG.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.ResultBadConfig.SystemNameserverCount">
+  <summary>
+    The number of nameservers in the system DNS config when the probe result was
+    BAD_CONFIG.
+  </summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.ResultNoInternet.Elapsed" units="ms">
+  <summary>Elapsed time of DNS probes that return PROBE_NO_INTERNET.</summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.ResultNxdomain.Elapsed" units="ms">
+  <summary>Elapsed time of DNS probes that return PROBE_NXDOMAIN.</summary>
+</histogram>
+
+<histogram name="DnsProbe.Probe.ResultUnknown.Elapsed" units="ms">
+  <summary>Elapsed time of DNS probes that return PROBE_UNKNOWN.</summary>
+</histogram>
+
 <histogram name="DomainBoundCerts.DBLoadedCount">
   <summary>Number of certs loaded from domain bound cert database.</summary>
 </histogram>
@@ -7427,6 +8318,64 @@ other types of suffix sets.
   <int value="3" label="LowMemory"/>
 </enum>
 
+<enum name="AsyncDNSConfigParsePosix" type="int">
+  <int value="0" label="OK"/>
+  <int value="1" label="RES_INIT_FAILED"/>
+  <int value="2" label="RES_INIT_UNSET"/>
+  <int value="3" label="BAD_ADDRESS"/>
+  <int value="4" label="BAD_EXT_STRUCT"/>
+  <int value="5" label="NULL_ADDRESS"/>
+  <int value="6" label="NO_NAMESERVERS"/>
+  <int value="7" label="MISSING_OPTIONS"/>
+  <int value="8" label="UNHANDLED_OPTIONS"/>
+</enum>
+
+<enum name="AsyncDNSConfigParseWin" type="int">
+  <int value="0" label="OK"/>
+  <int value="1" label="READ_IPHELPER"/>
+  <int value="2" label="READ_POLICY_SEARCHLIST"/>
+  <int value="3" label="READ_TCPIP_SEARCHLIST"/>
+  <int value="4" label="READ_DOMAIN"/>
+  <int value="5" label="READ_POLICY_DEVOLUTION"/>
+  <int value="6" label="READ_DNSCACHE_DEVOLUTION"/>
+  <int value="7" label="READ_TCPIP_DEVOLUTION"/>
+  <int value="8" label="READ_APPEND_MULTILABEL"/>
+  <int value="9" label="READ_PRIMARY_SUFFIX"/>
+  <int value="10" label="BAD_ADDRESS"/>
+  <int value="11" label="NO_NAMESERVERS"/>
+</enum>
+
+<enum name="AsyncDNSHostsParseWin" type="int">
+  <int value="0" label="OK"/>
+  <int value="1" label="UNREADABLE_HOSTS_FILE"/>
+  <int value="2" label="COMPUTER_NAME_FAILED"/>
+  <int value="3" label="IPHELPER_FAILED"/>
+  <int value="4" label="BAD_ADDRESS"/>
+</enum>
+
+<enum name="AsyncDNSParseResult" type="int">
+  <summary>Results of DnsResponse::ParseToAddressList.</summary>
+  <int value="0" label="SUCCESS"/>
+  <int value="1" label="MALFORMED_RESPONSE"/>
+  <int value="2" label="MALFORMED_CNAME"/>
+  <int value="3" label="NAME_MISMATCH"/>
+  <int value="4" label="SIZE_MISMATCH"/>
+  <int value="5" label="CNAME_AFTER_ADDRESS"/>
+  <int value="6" label="ADDRESS_TTL_MISMATCH"/>
+  <int value="7" label="NO_ADDRESSES"/>
+</enum>
+
+<enum name="AsyncDNSResolveStatus" type="int">
+  <int value="0" label="DNS_SUCCESS">Succeeded with async DNS.</int>
+  <int value="1" label="PROC_SUCCESS">
+    Succeeded with getaddrinfo after async DNS failed.
+  </int>
+  <int value="2" label="FAIL">Both async DNS and getaddrinfo failed.</int>
+  <int value="3" label="SUSPECT_NETBIOS">
+    Same as PROC_SUCCESS except the hostname fits NetBIOS name criteria.
+  </int>
+</enum>
+
 <enum name="AudioRendererEvents" type="int">
   <int value="0" label="Initialized"/>
   <int value="1" label="Runtime error"/>
@@ -7888,6 +8837,30 @@ other types of suffix sets.
   <int value="8" label="PlayMusic"/>
 </enum>
 
+<enum name="DnsProbe.Job.Result" type="int">
+  <int value="0" label="SERVERS_UNKNOWN"/>
+  <int value="1" label="SERVERS_CORRECT"/>
+  <int value="2" label="SERVERS_INCORRECT"/>
+  <int value="3" label="SERVERS_FAILING"/>
+  <int value="4" label="SERVERS_UNREACHABLE"/>
+</enum>
+
+<enum name="DnsProbe.Probe.Result" type="int">
+  <int value="0" label="UNKNOWN"/>
+  <int value="1" label="NO_INTERNET"/>
+  <int value="2" label="BAD_CONFIG"/>
+  <int value="3" label="NXDOMAIN"/>
+</enum>
+
+<enum name="DnsProbe.Probe.SystemIsLocalhost" type="int">
+  <int value="0" label="Not just 127.0.0.1">
+    127.0.0.1 was not the only nameserver in the system DNS config.
+  </int>
+  <int value="1" label="Just 127.0.0.1">
+    127.0.0.1 was the only nameserver in the system DNS config.
+  </int>
+</enum>
+
 <enum name="DomainBoundCerts.GetCertResult" type="int">
   <int value="0" label="SYNC_SUCCESS"/>
   <int value="1" label="ASYNC_SUCCESS"/>
@@ -10337,6 +11310,37 @@ other types of suffix sets.
   <int value="22" label="DOMAIN_NUM_EVENTS"/>
 </enum>
 
+<enum name="ResolutionCategory" type="int">
+  <int value="0" label="RESOLVE_SUCCESS"/>
+  <int value="1" label="RESOLVE_FAIL"/>
+  <int value="2" label="RESOLVE_SPECULATIVE_SUCCESS"/>
+  <int value="3" label="RESOLVE_SPECULATIVE_FAIL"/>
+</enum>
+
+<enum name="ResolutionUnspecWasteCategory" type="int">
+  <int value="0" label="AF_WASTE_IPV4_ONLY">
+    Running in a IPv4-only configuration.  No waste.
+  </int>
+  <int value="1" label="AF_WASTE_CACHE_IPV4">
+    Cache contained an UNSPEC result for this IPv4 lookup.  Waste.
+  </int>
+  <int value="2" label="AF_WASTE_CACHE_UNSPEC">
+    Cache contained an IPv4 result for this UNSPEC lookup.  Waste.
+  </int>
+  <int value="3" label="AF_WASTE_JOB_IPV4">
+    Job pool contained an UNSPEC job for this IPv4 lookup.  Waste.
+  </int>
+  <int value="4" label="AF_WASTE_JOB_UNSPEC">
+    Job pool contained an IPv4 job for this UNSPEC lookup.  Waste.
+  </int>
+  <int value="5" label="AF_WASTE_NONE_IPV4">
+    A new job was needed for this IPv4 lookup.  No waste.
+  </int>
+  <int value="6" label="AF_WASTE_NONE_UNSPEC">
+    A new job was needed for this UNSPEC lookup.  No waste.
+  </int>
+</enum>
+
 <enum name="SB2BloomFailure" type="int">
   <int value="0" label="READ_OPEN"/>
   <int value="1" label="READ_VERSION"/>
@@ -11216,64 +12220,26 @@ other types of suffix sets.
   <affected-histogram name="Cros.ClickOnShelf"/>
 </fieldtrial>
 
-<fieldtrial name="DnsImpact2">
-  <group name="disabled_prefetch"
-      label="DNS pre-resolving is disabled in these clients"/>
-  <group name="disabled_prefetch_4_connections"
-      label="DNS pre-resolving is disabled in these clients, and a maximum of
-             4 connections per host was allowed"/>
-  <group name="enabled_prefetch_4_connections"
-      label="a maximum of 4 connections per host was allowed in these clients"/>
-  <group name="parallel_4_prefetch"
-      label="DNS pre-resolving was only doing 4 concurrent speculative
-             resolutions in this test"/>
-  <affected-histogram name="Net.Dns_Resolution_And_TCP_Connection_Latency"/>
-  <affected-histogram name="Net.TCP_Connection_Idle_Sockets">
-    <with-group name="disabled_prefetch"/>
-    <with-group name="disabled_prefetch_4_connections"/>
-    <with-group name="enabled_prefetch_4_connections"/>
-  </affected-histogram>
-  <affected-histogram name="Net.TCP_Connection_Latency"/>
-  <affected-histogram name="Net.Transaction_Connected"/>
-  <affected-histogram name="Net.Transaction_Connected_New"/>
-  <affected-histogram name="Net.Transaction_Connected_New_b"/>
-  <affected-histogram name="Net.Transaction_Connected_Under_10"/>
-  <affected-histogram name="Net.Transaction_Latency"/>
-  <affected-histogram name="Net.Transaction_Latency_b"/>
-  <affected-histogram name="Net.Transaction_Latency_Total"/>
-  <affected-histogram name="Net.Transaction_Latency_Total_New_Connection"/>
-  <affected-histogram
-      name="Net.Transaction_Latency_Total_New_Connection_Under_10"/>
-  <affected-histogram name="Net.Transaction_Latency_Total_Under_10"/>
-  <affected-histogram name="Net.Transaction_Latency_Under_10"/>
-  <affected-histogram name="PLT.RequestToFinish">
-    <with-group name="parallel_4_prefetch"/>
-  </affected-histogram>
-</fieldtrial>
-
-<fieldtrial name="DnsImpact3">
-  <group name="disabled_prefetch" label="with DNS pre-resolving disabled"/>
-  <group name="parallel_4_prefetch"
-      label="with only 4 concurrent speculative resolutions done in parallel"/>
-  <affected-histogram name="Net.Transaction_Connected_New">
-    <with-group name="disabled_prefetch"/>
-  </affected-histogram>
-  <affected-histogram name="Renderer2.FinishDocToFinish"/>
-  <affected-histogram name="Renderer2.RequestToFinish"/>
-  <affected-histogram name="Renderer2.RequestToFinish_L">
-    <with-group name="disabled_prefetch"/>
-  </affected-histogram>
-  <affected-histogram name="Renderer2.RequestToFirstLayout"/>
-  <affected-histogram name="Renderer2.RequestToStart"/>
-  <affected-histogram name="Renderer2.StartToFinish"/>
-  <affected-histogram name="Renderer2.StartToFinishDoc"/>
-  <affected-histogram name="Renderer2.StartToFirstLayout"/>
-  <affected-histogram name="Renderer4.RequestToFinish">
-    <with-group name="parallel_4_prefetch"/>
-  </affected-histogram>
-  <affected-histogram name="Renderer4.StartToFinish">
-    <with-group name="parallel_4_prefetch"/>
-  </affected-histogram>
+<fieldtrial name="DnsParallelism">
+  <group name="parallel_10"
+      label="with only 10 concurrent resolutions done in parallel"/>
+  <group name="parallel_14"
+      label="with only 14 concurrent resolutions done in parallel"/>
+  <group name="parallel_20"
+      label="with only 20 concurrent resolutions done in parallel"/>
+  <group name="parallel_6"
+      label="with only 6 concurrent resolutions done in parallel"/>
+  <group name="parallel_7"
+      label="with only 7 concurrent resolutions done in parallel"/>
+  <group name="parallel_8"
+      label="with only 8 concurrent resolutions done in parallel"/>
+  <group name="parallel_9"
+      label="with only 9 concurrent resolutions done in parallel"/>
+  <group name="parallel_default"
+      label="with the default number of concurrent resolutions done in
+             parallel"/>
+  <affected-histogram name="DNS.ResolveCategory"/>
+  <affected-histogram name="DNS.ResolveSuccess"/>
 </fieldtrial>

[Ilya Sherman, 2013/05/13 22:59:50]

Please make this CL purely a copy/paste out of the internal file, and split off
the change to remove these field trials to a separate, follow-up CL.

[mef, 2013/05/14 15:55:03]

Done.

 
 <fieldtrial name="DomainGoogle" separator="">
@@ -11329,6 +12295,14 @@ other types of suffix sets.
   <affected-histogram name="Instant.SessionsStorageNamespace"/>
 </fieldtrial>
 
+<fieldtrial name="IPv6_Probe">
+  <group name="IPv6_probe_skipped"
+      label="with IPv6 not probed, and default OS settings used"/>
+  <group name="IPv6_probe_done"
+      label="with IPv6 probed for and possibly disabled"/>
+  <affected-histogram name="DNS.PrefetchResolution"/>
+</fieldtrial>
+
 <fieldtrial name="LateBindingExperiment">
   <group name="disable_late_binding" label="socket late binding is disabled"/>
   <group name="enable_late_binding" label="socket late binding is enabled"/>