Supporting command line argument to force field trials

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index cce078682c0229ab06e2bcdd228ec0f23924427c..875e0db6eeeebedae21c59ad39ab6505b2588898 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -592,6 +592,20 @@ void ChromeBrowserMainParts::SetupMetricsAndFieldTrials() {
     metrics->ForceClientIdCreation();  // Needed below.
   field_trial_list_.reset(new base::FieldTrialList(metrics->GetClientId()));
 
+  // Ensure any field trials specified on the command line are initialized.
+  // Also stop the metrics service so that we don't pollute UMA.

[jar (doing other things), 2012/04/06 01:41:29]

I'm not sure on the ordering, but disabling UMA is probably better done around
line 1095.  You might need to separate the setting of field trials, from the
control of UMA as well.

[MAD, 2012/04/11 02:38:08]

Done.

+#ifndef NDEBUG
+  const CommandLine* command_line = CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kForceFieldTestNameAndValue)) {
+    std::string persistent = command_line->GetSwitchValueASCII(
+        switches::kForceFieldTestNameAndValue);
+    bool ret = base::FieldTrialList::CreateTrialsFromString(persistent);
+    CHECK(ret) << "Invalid --" << switches::kForceFieldTestNameAndValue <<
+                  " list specified.";
+    metrics->Stop();
+  }
+#endif  // NDEBUG
+
   SetupFieldTrials(metrics->recording_active(),
                    local_state_->IsManagedPreference(
                        prefs::kMaxConnectionsPerProxy));
@@ -613,16 +627,17 @@ void ChromeBrowserMainParts::ConnectionFieldTrial() {
   const base::FieldTrial::Probability kConnectDivisor = 100;
   const base::FieldTrial::Probability kConnectProbability = 1;  // 1% prob.
 
-  // After June 30, 2011 builds, it will always be in default group.
-  scoped_refptr<base::FieldTrial> connect_trial(
-      new base::FieldTrial(
-          "ConnCountImpact", kConnectDivisor, "conn_count_6", 2011, 6, 30));
-
   // This (6) is the current default value. Having this group declared here
   // makes it straightforward to modify |kConnectProbability| such that the same
   // probability value will be assigned to all the other groups, while
   // preserving the remainder of the of probability space to the default value.
-  const int connect_6 = connect_trial->kDefaultGroupNumber;
+  int connect_6 = -1;
+
+  // After June 30, 2011 builds, it will always be in default group.
+  scoped_refptr<base::FieldTrial> connect_trial(
+      base::FieldTrialList::GetFieldTrialInstance(
+          "ConnCountImpact", kConnectDivisor, "conn_count_6", &connect_6,
+          2011, 6, 30));
 
   const int connect_5 = connect_trial->AppendGroup("conn_count_5",
                                                    kConnectProbability);
@@ -667,10 +682,11 @@ void ChromeBrowserMainParts::SocketTimeoutFieldTrial() {
   const base::FieldTrial::Probability kSocketTimeoutProbability = 1;
 
   // After June 30, 2011 builds, it will always be in default group.
+  int socket_timeout_10 = -1;
   scoped_refptr<base::FieldTrial> socket_timeout_trial(
-      new base::FieldTrial("IdleSktToImpact", kIdleSocketTimeoutDivisor,
-          "idle_timeout_10", 2011, 6, 30));
-  const int socket_timeout_10 = socket_timeout_trial->kDefaultGroupNumber;
+      base::FieldTrialList::GetFieldTrialInstance(
+          "IdleSktToImpact", kIdleSocketTimeoutDivisor, "idle_timeout_10",
+          &socket_timeout_10, 2011, 6, 30));
 
   const int socket_timeout_5 =
       socket_timeout_trial->AppendGroup("idle_timeout_5",
@@ -700,16 +716,17 @@ void ChromeBrowserMainParts::ProxyConnectionsFieldTrial() {
   // 25% probability
   const base::FieldTrial::Probability kProxyConnectionProbability = 1;
 
-  // After June 30, 2011 builds, it will always be in default group.
-  scoped_refptr<base::FieldTrial> proxy_connection_trial(
-      new base::FieldTrial("ProxyConnectionImpact", kProxyConnectionsDivisor,
-          "proxy_connections_32", 2011, 6, 30));
-
   // This (32 connections per proxy server) is the current default value.
   // Declaring it here allows us to easily re-assign the probability space while
   // maintaining that the default group always has the remainder of the "share",
   // which allows for cleaner and quicker changes down the line if needed.
-  const int proxy_connections_32 = proxy_connection_trial->kDefaultGroupNumber;
+  int proxy_connections_32 = -1;
+
+  // After June 30, 2011 builds, it will always be in default group.
+  scoped_refptr<base::FieldTrial> proxy_connection_trial(
+      base::FieldTrialList::GetFieldTrialInstance(
+          "ProxyConnectionImpact", kProxyConnectionsDivisor,
+          "proxy_connections_32", &proxy_connections_32, 2011, 6, 30));
 
   // The number of max sockets per group cannot be greater than the max number
   // of sockets per proxy server.  We tried using 8, and it can easily
@@ -767,13 +784,14 @@ void ChromeBrowserMainParts::SpdyFieldTrial() {
     base::FieldTrial::Probability flow_control_probability = 5;
     base::FieldTrial::Probability spdy3_probability = 0;
 
+    // NPN with spdy support is the default.
+    int npn_spdy_grp = -1;
+
     // After June 30, 2013 builds, it will always be in default group.
     scoped_refptr<base::FieldTrial> trial(
-        new base::FieldTrial(
-            "SpdyImpact", kSpdyDivisor, "npn_with_spdy", 2013, 6, 30));
-
-    // NPN with spdy support is the default.
-    int npn_spdy_grp = trial->kDefaultGroupNumber;
+        base::FieldTrialList::GetFieldTrialInstance(
+            "SpdyImpact", kSpdyDivisor, "npn_with_spdy", &npn_spdy_grp,
+            2013, 6, 30));
 
     // NPN with only http support, no spdy.
     int npn_http_grp = trial->AppendGroup("npn_with_http", npnhttp_probability);
@@ -817,8 +835,8 @@ void ChromeBrowserMainParts::SpdyFieldTrial() {
   // After June 30, 2013 builds, it will always be in default group
   // (cwndDynamic).
   scoped_refptr<base::FieldTrial> trial(
-      new base::FieldTrial(
-          "SpdyCwnd", kSpdyCwndDivisor, "cwndDynamic", 2013, 6, 30));
+      base::FieldTrialList::GetFieldTrialInstance(
+          "SpdyCwnd", kSpdyCwndDivisor, "cwndDynamic", NULL, 2013, 6, 30));
 
   trial->AppendGroup("cwnd10", kSpdyCwnd10);
   trial->AppendGroup("cwnd16", kSpdyCwnd16);
@@ -854,14 +872,15 @@ void ChromeBrowserMainParts::WarmConnectionFieldTrial() {
   const base::FieldTrial::Probability kWarmSocketDivisor = 100;
   const base::FieldTrial::Probability kWarmSocketProbability = 33;
 
+  // Default value is USE_LAST_ACCESSED_SOCKET.
+  int last_accessed_socket = -1;
+
   // After January 30, 2013 builds, it will always be in default group.
   scoped_refptr<base::FieldTrial> warmest_socket_trial(
-      new base::FieldTrial(
+      base::FieldTrialList::GetFieldTrialInstance(
           "WarmSocketImpact", kWarmSocketDivisor, "last_accessed_socket",
-          2013, 1, 30));
+          &last_accessed_socket, 2013, 1, 30));
 
-  // Default value is USE_LAST_ACCESSED_SOCKET.
-  const int last_accessed_socket = warmest_socket_trial->kDefaultGroupNumber;
   const int warmest_socket = warmest_socket_trial->AppendGroup(
       "warmest_socket", kWarmSocketProbability);
   const int warm_socket = warmest_socket_trial->AppendGroup(
@@ -891,11 +910,11 @@ void ChromeBrowserMainParts::ConnectBackupJobsFieldTrial() {
     // 1% probability.
     const base::FieldTrial::Probability kConnectBackupJobsProbability = 1;
     // After June 30, 2011 builds, it will always be in default group.
+    int connect_backup_jobs_enabled = -1;
     scoped_refptr<base::FieldTrial> trial(
-        new base::FieldTrial("ConnnectBackupJobs",
-            kConnectBackupJobsDivisor, "ConnectBackupJobsEnabled", 2011, 6,
-                30));
-    const int connect_backup_jobs_enabled = trial->kDefaultGroupNumber;
+        base::FieldTrialList::GetFieldTrialInstance("ConnnectBackupJobs",
+            kConnectBackupJobsDivisor, "ConnectBackupJobsEnabled",
+            &connect_backup_jobs_enabled, 2011, 6, 30));
     trial->AppendGroup("ConnectBackupJobsDisabled",
                        kConnectBackupJobsProbability);
     const int trial_group = trial->group();
@@ -913,8 +932,9 @@ void ChromeBrowserMainParts::PredictorFieldTrial() {
   // After June 30, 2011 builds, it will always be in default group
   // (default_enabled_prefetch).
   scoped_refptr<base::FieldTrial> trial(
-      new base::FieldTrial("DnsImpact", kDivisor,
-                           "default_enabled_prefetch", 2011, 10, 30));
+      base::FieldTrialList::GetFieldTrialInstance(
+          "DnsImpact", kDivisor, "default_enabled_prefetch", NULL,
+          2011, 10, 30));
 
   // First option is to disable prefetching completely.
   int disabled_prefetch = trial->AppendGroup("disabled_prefetch",
@@ -1021,8 +1041,8 @@ void ChromeBrowserMainParts::ComodoDNSExperimentFieldTrial() {
 
   // After April 15, 2012 builds, it will always be in default group.
   scoped_refptr<base::FieldTrial> trial(
-      new base::FieldTrial("ComodoDNSExperiment", kDivisor,
-          "inactive", 2012, 4, 15));
+      base::FieldTrialList::GetFieldTrialInstance(
+          "ComodoDNSExperiment", kDivisor, "inactive", NULL, 2012, 4, 15));
 
   const int active = trial->AppendGroup("active", kProbability);
 
@@ -1668,10 +1688,11 @@ int ChromeBrowserMainParts::PreMainMessageLoopRunImpl() {
     base::FieldTrial::Probability kSDCH_DIVISOR = 1000;
     base::FieldTrial::Probability kSDCH_DISABLE_PROBABILITY = 1;  // 0.1% prob.
     // After March 31, 2012 builds, it will always be in default group.
+    int sdch_enabled_group = -1;
     scoped_refptr<base::FieldTrial> sdch_trial(
-        new base::FieldTrial("GlobalSdch", kSDCH_DIVISOR, "global_enable_sdch",
-            2012, 3, 31));
-    int sdch_enabled_group = sdch_trial->kDefaultGroupNumber;
+        base::FieldTrialList::GetFieldTrialInstance(
+            "GlobalSdch", kSDCH_DIVISOR, "global_enable_sdch",
+            &sdch_enabled_group, 2012, 3, 31));
 
     sdch_trial->AppendGroup("global_disable_sdch",
                             kSDCH_DISABLE_PROBABILITY);