Add telemetry to track the time an event spent waiting for the main thread.

content/browser/renderer_host/render_widget_host_impl.h

Index: content/browser/renderer_host/render_widget_host_impl.h
diff --git a/content/browser/renderer_host/render_widget_host_impl.h b/content/browser/renderer_host/render_widget_host_impl.h
index 362c6d7f793f0b0405da6e7651f897d54e3217b2..f03469a4a8b4d6ca0e59ef9eb03ee4357d318d05 100644
--- a/content/browser/renderer_host/render_widget_host_impl.h
+++ b/content/browser/renderer_host/render_widget_host_impl.h
@@ -735,7 +735,7 @@ class CONTENT_EXPORT RenderWidgetHostImpl : virtual public RenderWidgetHost,
                                InputEventAckState ack_result) OVERRIDE;
   virtual void OnTouchEventAck(const TouchEventWithLatencyInfo& event,
                                InputEventAckState ack_result) OVERRIDE;
-  virtual void OnGestureEventAck(const WebKit::WebGestureEvent& event,
+  virtual void OnGestureEventAck(const GestureEventWithLatencyInfo& event,
                                  InputEventAckState ack_result) OVERRIDE;
   virtual void OnUnexpectedEventAck(bool bad_message) OVERRIDE;
 
@@ -745,6 +745,10 @@ class CONTENT_EXPORT RenderWidgetHostImpl : virtual public RenderWidgetHost,
   // which may get in recursive loops).
   void DelayedAutoResized();
 
+  // Helper function to record impl thread to main thread event latency.
+  void UpdateRenderingStatsForImplThreadLatency(
+      WebKit::WebInputEvent::Type type,
+      const ui::LatencyInfo& latency_info);
 
   // Our delegate, which wants to know mainly about keyboard events.
   // It will remain non-NULL until DetachDelegate() is called.