[net/dns] Instrument DnsConfigService to measure performance and failures.

net/dns/dns_config_service.cc

Index: net/dns/dns_config_service.cc
diff --git a/net/dns/dns_config_service.cc b/net/dns/dns_config_service.cc
index 43acf481007349962f73a8c31f82e1cd510313cf..a520d261b9dbe6ac2f53a5e786ff766eeb55634f 100644
--- a/net/dns/dns_config_service.cc
+++ b/net/dns/dns_config_service.cc
@@ -152,6 +152,12 @@ void DnsConfigService::Watch(const CallbackType& callback) {
 
 void DnsConfigService::InvalidateConfig() {
   DCHECK(CalledOnValidThread());
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (!last_invalidate_config_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.ConfigNotifyInterval",
+                             now - last_invalidate_config_time_);
+  }
+  last_invalidate_config_time_ = now;
   if (!have_config_)
     return;
   have_config_ = false;
@@ -160,6 +166,12 @@ void DnsConfigService::InvalidateConfig() {
 
 void DnsConfigService::InvalidateHosts() {
   DCHECK(CalledOnValidThread());
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (!last_invalidate_hosts_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.HostsNotifyInterval",
+                             now - last_invalidate_hosts_time_);
+  }
+  last_invalidate_hosts_time_ = now;
   if (!have_hosts_)
     return;
   have_hosts_ = false;
@@ -170,10 +182,17 @@ void DnsConfigService::OnConfigRead(const DnsConfig& config) {
   DCHECK(CalledOnValidThread());
   DCHECK(config.IsValid());
 
+  bool changed = false;
   if (!config.EqualsIgnoreHosts(dns_config_)) {
     dns_config_.CopyIgnoreHosts(config);
     need_update_ = true;
+    changed = true;
   }
+  if (!changed && !last_sent_empty_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.UnchangedConfigInterval",
+                             base::TimeTicks::Now() - last_sent_empty_time_);
+  }
+  UMA_HISTOGRAM_BOOLEAN("AsyncDNS.ConfigChange", changed);
 
   have_config_ = true;
   if (have_hosts_)
@@ -183,10 +202,17 @@ void DnsConfigService::OnConfigRead(const DnsConfig& config) {
 void DnsConfigService::OnHostsRead(const DnsHosts& hosts) {
   DCHECK(CalledOnValidThread());
 
+  bool changed = false;
   if (hosts != dns_config_.hosts) {
     dns_config_.hosts = hosts;
     need_update_ = true;
+    changed = true;
+  }
+  if (!changed && !last_sent_empty_time_.is_null()) {
+    UMA_HISTOGRAM_LONG_TIMES("AsyncDNS.UnchangedHostsInterval",
+                             base::TimeTicks::Now() - last_sent_empty_time_);
   }
+  UMA_HISTOGRAM_BOOLEAN("AsyncDNS.HostsChange", changed);
 
   have_hosts_ = true;
   if (have_config_)
@@ -226,6 +252,7 @@ void DnsConfigService::OnTimeout() {
   need_update_ = true;
   // Empty config is considered invalid.
   last_sent_empty_ = true;
+  last_sent_empty_time_ = base::TimeTicks::Now();
   callback_.Run(DnsConfig());
 }