Send all field trials from the browser.

chrome/renderer/chrome_render_process_observer.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/renderer/chrome_render_process_observer.h"
 
 #include <limits>
 #include <vector>
 
 #include "base/allocator/allocator_extension.h"
@@ skipping 281 matching lines @@
   // after we engage the sandbox.
   if (!command_line.HasSwitch(switches::kSingleProcess))
     crypto::InitNSSSafely();
 #elif defined(OS_WIN)
   // crypt32.dll is used to decode X509 certificates for Chromoting.
   // Only load this library when the feature is enabled.
   base::LoadNativeLibrary(base::FilePath(L"crypt32.dll"), NULL);
 #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() {
 }
 
 bool ChromeRenderProcessObserver::OnControlMessageReceived(
     const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(ChromeRenderProcessObserver, message)
     IPC_MESSAGE_HANDLER(ChromeViewMsg_SetIsIncognitoProcess,
@@ skipping 46 matching lines @@
   RenderThread::Get()->Send(new ChromeViewHostMsg_ResourceTypeStats(stats));
 }
 
 void ChromeRenderProcessObserver::OnSetFieldTrialGroup(
     const std::string& field_trial_name,
     const std::string& group_name) {
   base::FieldTrial* trial =
       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();
 }
 
 void ChromeRenderProcessObserver::OnGetV8HeapStats() {
   HeapStatisticsCollector::Instance()->InitiateCollection();
 }
 
 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));
+}