Do not register synthetic field trial before initializing TaskScheduler.

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 81b1a58a590f42cbb940b96151fd309e0351467e..311cf340e24ec7ac426cbe27bfe5a565e90a5164 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -878,37 +878,11 @@ void ChromeBrowserMainParts::SetupFieldTrials() {
   // This must be called after |local_state_| is initialized.
   browser_field_trials_.SetupFieldTrials();
 
-  // Enable Navigation Tracing only if a trace upload url is specified.
-  if (command_line->HasSwitch(switches::kEnableNavigationTracing) &&
-      command_line->HasSwitch(switches::kTraceUploadURL)) {
-    tracing::SetupNavigationTracing();
-  }
-
   // Initialize FieldTrialSynchronizer system. This is a singleton and is used
   // for posting tasks via base::Bind. Its deleted when it goes out of scope.
   // Even though base::Bind does AddRef and Release, the object will not be
   // deleted after the Task is executed.
   field_trial_synchronizer_ = new FieldTrialSynchronizer();
-
-  // Register a synthetic field trial for the sampling profiler configuration
-  // that was already chosen.
-  sampling_profiler_config_.RegisterSyntheticFieldTrial();
-
-#if defined(OS_WIN) || defined(OS_MACOSX) || \
-    (defined(OS_LINUX) && !defined(OS_CHROMEOS))
-  metrics::DesktopSessionDurationTracker::Initialize();
-#endif
-
-#if defined(OS_WIN)
-  // Cleanup the PreRead field trial registry key.
-  // TODO(fdoray): Remove this when M56 hits stable.
-  const base::string16 pre_read_field_trial_registry_path =
-      BrowserDistribution::GetDistribution()->GetRegistryPath() +
-      L"\\PreReadFieldTrial";
-  base::win::RegKey(HKEY_CURRENT_USER,
-                    pre_read_field_trial_registry_path.c_str(), KEY_SET_VALUE)
-      .DeleteKey(L"");
-#endif  // defined(OS_WIN)
 }
 
 void ChromeBrowserMainParts::SetupMetrics() {
@@ -934,6 +908,19 @@ void ChromeBrowserMainParts::SetupMetrics() {
       // Don't enable instrumentation.
       break;
   }
+
+  // Enable Navigation Tracing only if a trace upload url is specified.
+  const base::CommandLine* command_line =
+      base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kEnableNavigationTracing) &&
+      command_line->HasSwitch(switches::kTraceUploadURL)) {
+    tracing::SetupNavigationTracing();

[robliao, 2016/09/30 01:10:09]

This section seems like it could go outside of SetupMetrics. Is this triggering
issues?

[fdoray, 2016/09/30 12:36:42]

No longer changing this section in this CL.

+  }
+
+#if defined(OS_WIN) || defined(OS_MACOSX) || \
+    (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+  metrics::DesktopSessionDurationTracker::Initialize();
+#endif
 }
 
 void ChromeBrowserMainParts::StartMetricsRecording() {
@@ -942,6 +929,11 @@ void ChromeBrowserMainParts::StartMetricsRecording() {
   g_browser_process->metrics_service()->CheckForClonedInstall(
       BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE));
 
+  // Register a synthetic field trial for the sampling profiler configuration
+  // that was already chosen. This must be done before the line below creates
+  // the first MetricsLog.
+  sampling_profiler_config_.RegisterSyntheticFieldTrial();
+
   g_browser_process->GetMetricsServicesManager()->UpdateUploadPermissions(true);
 }
 
@@ -1531,6 +1523,17 @@ void ChromeBrowserMainParts::PostBrowserStart() {
   }
 #endif
 
+#if defined(OS_WIN)
+  // Cleanup the PreRead field trial registry key.
+  // TODO(fdoray): Remove this when M56 hits stable.
+  const base::string16 pre_read_field_trial_registry_path =

[robliao, 2016/09/30 01:10:09]

Can this be done in a separate CL?

[fdoray, 2016/09/30 12:36:41]

Done. Made the CL smaller.

+      BrowserDistribution::GetDistribution()->GetRegistryPath() +
+      L"\\PreReadFieldTrial";
+  base::win::RegKey(HKEY_CURRENT_USER,
+                    pre_read_field_trial_registry_path.c_str(), KEY_SET_VALUE)
+      .DeleteKey(L"");
+#endif  // defined(OS_WIN)
+
   // At this point, StartupBrowserCreator::Start has run creating initial
   // browser windows and tabs, but no progress has been made in loading
   // content as the main message loop hasn't started processing tasks yet.