Send all field trials from the browser.

chrome/browser/renderer_host/chrome_render_message_filter.cc

Index: chrome/browser/renderer_host/chrome_render_message_filter.cc
diff --git a/chrome/browser/renderer_host/chrome_render_message_filter.cc b/chrome/browser/renderer_host/chrome_render_message_filter.cc
index 7595229741abd52383bc4c03f3c907a1a048d11a..aaa7476cf929b5bd60d06b56cac6d70b0f882463 100644
--- a/chrome/browser/renderer_host/chrome_render_message_filter.cc
+++ b/chrome/browser/renderer_host/chrome_render_message_filter.cc
@@ -8,6 +8,7 @@
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/content_settings/cookie_settings.h"
@@ -82,6 +83,8 @@ bool ChromeRenderMessageFilter::OnMessageReceived(const IPC::Message& message) {
     IPC_MESSAGE_HANDLER(ChromeViewHostMsg_IsCrashReportingEnabled,
                         OnIsCrashReportingEnabled)
 #endif
+    IPC_MESSAGE_HANDLER(ChromeViewHostMsg_FieldTrialActivated,
+                        OnFieldTrialActivated)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
@@ -361,3 +364,10 @@ void ChromeRenderMessageFilter::OnIsCrashReportingEnabled(bool* enabled) {
   *enabled = ChromeMetricsServiceAccessor::IsCrashReportingEnabled();
 }
 #endif
+
+void ChromeRenderMessageFilter::OnFieldTrialActivated(
+    const std::string& trial_name,
+    const std::string& group_name) {
+  // Activate trial by calling FinFullName.

[Alexei Svitkine (slow), 2014/11/07 15:51:02]

Nit: You have a typo in the comment. However, a better comment would mention the
reason we're doing this.

e.g.

// Active the trial in the browser process to match its state in the renderer.

[Georges Khalil, 2014/11/07 16:44:23]

Done.

+  base::FieldTrialList::FindFullName(trial_name);
+}