Send all field trials from the browser.

chrome/renderer/chrome_render_process_observer.cc

Index: chrome/renderer/chrome_render_process_observer.cc
diff --git a/chrome/renderer/chrome_render_process_observer.cc b/chrome/renderer/chrome_render_process_observer.cc
index ad3ab00752622ce4fcea20b1507a76a41ad8bb7e..d0ed608f3c9d8ed0b2fd03424ec8b4e6fe161b6f 100644
--- a/chrome/renderer/chrome_render_process_observer.cc
+++ b/chrome/renderer/chrome_render_process_observer.cc
@@ -299,6 +299,8 @@ ChromeRenderProcessObserver::ChromeRenderProcessObserver(
 #endif
   // Setup initial set of crash dump data for Field Trials in this renderer.
   chrome_variations::SetChildProcessLoggingVariationList();
+  // Report any field trials activations to the browser.

[Alexei Svitkine (slow), 2014/11/05 22:50:53]

Nit: I would make the comment say "// Listen for field trial activations to
report them to the browser."

[Georges Khalil, 2014/11/06 18:36:28]

Done.

+  base::FieldTrialList::AddObserver(this);
 }
 
 ChromeRenderProcessObserver::~ChromeRenderProcessObserver() {
@@ -365,8 +367,8 @@ void ChromeRenderProcessObserver::OnSetFieldTrialGroup(
       base::FieldTrialList::CreateFieldTrial(field_trial_name, group_name);
   // TODO(mef): Remove this check after the investigation of 359406 is complete.
   CHECK(trial) << field_trial_name << ":" << group_name;
-  // Ensure the trial is marked as "used" by calling group() on it. This is
-  // needed to ensure the trial is properly reported in renderer crash reports.
+  // Ensure the trial is marked as "used" by calling group() on it if it is
+  // marked as activated.
   trial->group();
   chrome_variations::SetChildProcessLoggingVariationList();
 }
@@ -379,3 +381,10 @@ const RendererContentSettingRules*
 ChromeRenderProcessObserver::content_setting_rules() const {
   return &content_setting_rules_;
 }
+
+void ChromeRenderProcessObserver::OnFieldTrialGroupFinalized(
+    const std::string& trial_name,
+    const std::string& group_name) {
+  content::RenderThread::Get()->Send(
+      new ChromeViewHostMsg_FieldTrialActivated(trial_name, group_name));
+}