Convert FieldTrialActivated to use mojo.

chrome/renderer/chrome_render_thread_observer.cc

Index: chrome/renderer/chrome_render_thread_observer.cc
diff --git a/chrome/renderer/chrome_render_thread_observer.cc b/chrome/renderer/chrome_render_thread_observer.cc
index fca78967da123fb0a3e3df76b658ef41644f82da..bb026dcae21521955a564d2f18cbc2df9a2501c2 100644
--- a/chrome/renderer/chrome_render_thread_observer.cc
+++ b/chrome/renderer/chrome_render_thread_observer.cc
@@ -46,6 +46,7 @@
 #include "mojo/public/cpp/bindings/strong_binding.h"
 #include "net/base/net_errors.h"
 #include "net/base/net_module.h"
+#include "services/service_manager/public/cpp/interface_provider.h"
 #include "services/service_manager/public/cpp/interface_registry.h"
 #include "third_party/WebKit/public/web/WebCache.h"
 #include "third_party/WebKit/public/web/WebDocument.h"
@@ -292,8 +293,10 @@ void ChromeRenderThreadObserver::OnRenderProcessShutdown() {
 void ChromeRenderThreadObserver::OnFieldTrialGroupFinalized(
     const std::string& trial_name,
     const std::string& group_name) {
-  content::RenderThread::Get()->Send(
-      new ChromeViewHostMsg_FieldTrialActivated(trial_name));
+  if (!field_trial_recorder_)

[Sam McNally, 2016/11/07 06:56:54]

OnFieldTrialGroupFinalized seems like it should only be called once per process,
so |field_trial_recorder_| can just be a local. Otherwise, resetting
|field_trial_recorder_| in OnRenderProcessShutdown() above should fix your
single-process test threading issues.

[nigeltao1, 2016/11/10 06:23:04]

I made it a local.

+    content::RenderThread::Get()->GetRemoteInterfaces()->GetInterface(
+        &field_trial_recorder_);
+  field_trial_recorder_->FieldTrialActivated(trial_name);
 }
 
 void ChromeRenderThreadObserver::OnSetIsIncognitoProcess(