Convert FieldTrialActivated to use mojo.

chrome/renderer/chrome_render_thread_observer.h

Index: chrome/renderer/chrome_render_thread_observer.h
diff --git a/chrome/renderer/chrome_render_thread_observer.h b/chrome/renderer/chrome_render_thread_observer.h
index 3e377bb4f905ffd8807bac38c7f11188a37179b0..118745ed6bd94964018002f2a97164b6a2175b77 100644
--- a/chrome/renderer/chrome_render_thread_observer.h
+++ b/chrome/renderer/chrome_render_thread_observer.h
@@ -12,6 +12,7 @@
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/metrics/field_trial.h"
+#include "chrome/common/field_trial_recorder.mojom.h"
 #include "chrome/common/variations/child_process_field_trial_syncer.h"
 #include "components/content_settings/core/common/content_settings.h"
 #include "content/public/renderer/render_thread_observer.h"
@@ -75,6 +76,7 @@ class ChromeRenderThreadObserver : public content::RenderThreadObserver,
   static bool is_incognito_process_;
   std::unique_ptr<content::ResourceDispatcherDelegate> resource_delegate_;
   RendererContentSettingRules content_setting_rules_;
+  chrome::mojom::FieldTrialRecorderPtr field_trial_recorder_;
   chrome_variations::ChildProcessFieldTrialSyncer field_trial_syncer_;
 
   std::unique_ptr<visitedlink::VisitedLinkSlave> visited_link_slave_;