Add input latency histograms for wheel events

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 41df865165ec7b2313b939a62ae5f774dd3edc8f..8d86da8b8712908f7dc4d85e283489fa27427fd2 100644
--- a/content/browser/renderer_host/render_widget_host_impl.h
+++ b/content/browser/renderer_host/render_widget_host_impl.h
@@ -437,7 +437,6 @@ class CONTENT_EXPORT RenderWidgetHostImpl
   // other way around.
   bool should_auto_resize() { return should_auto_resize_; }
 
-  void ComputeTouchLatency(const ui::LatencyInfo& latency_info);
   void FrameSwapped(const ui::LatencyInfo& latency_info);
   void DidReceiveRendererFrame();
 
@@ -483,11 +482,14 @@ class CONTENT_EXPORT RenderWidgetHostImpl
   // Create a LatencyInfo struct with INPUT_EVENT_LATENCY_RWH_COMPONENT
   // component if it is not already in |original|. And if |original| is
   // not NULL, it is also merged into the resulting LatencyInfo.
-  ui::LatencyInfo CreateRWHLatencyInfoIfNotExist(
+  ui::LatencyInfo CreateInputEventLatencyInfoIfNotExist(

[Yufeng Shen (Slow to review), 2014/10/28 18:02:25]

why do you need to change the name ?

[ccameron, 2014/10/28 23:18:28]

It relates to input, and that wasn't in the name. The fact that it's RWH-centric
is clear from the fact that this is RenderWidgetHostImpl.

Let me know if you'd prefer another name.

       const ui::LatencyInfo* original,
       blink::WebInputEvent::Type type,
       const ui::LatencyInfo::InputCoordinate* logical_coordinates,
       size_t logical_coordinates_size);
+  void ComputeInputLatencyHistograms(

[jdduke (slow), 2014/10/29 01:47:37]

Could be wrong, but I don't think this needs to be a member function. Can we
make it a free function in the .cc file anon namespace? Can you also use a const
char* arg type for the name?

[ccameron, 2014/10/29 02:09:02]

It calls to GetLatencyComponentId, which is a member function.

Changed to const char*.

[jdduke (slow), 2014/10/29 02:18:37]

Could you pass GetLatencyComponentId() to the function? RWHI has enough going on
that isolating these latency methods (and potential side effects) will almost
always be a win =/.

[ccameron, 2014/10/29 03:29:41]

I've marked this function const, to indicate that it does not mutate the object.

+      const std::string& event_type_name,
+      const ui::LatencyInfo& latency_info);
 
   // Called when we receive a notification indicating that the renderer
   // process has gone. This will reset our state so that our state will be