Notify WebContentsObservers of user interactions.

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 bd6bc767fc252f6b9acf9d617dd9154aa94a1471..226d06f573363fc542cd2f0b18b40441ffabb65f 100644
--- a/content/browser/renderer_host/render_widget_host_impl.h
+++ b/content/browser/renderer_host/render_widget_host_impl.h
@@ -578,6 +578,11 @@ class CONTENT_EXPORT RenderWidgetHostImpl : public RenderWidgetHost,
   // NotifyRendererResponsive.
   void RendererIsResponsive();
 
+  // Notification that the user has made some kind of direct input with the
+  // page. Direct input includes 1) any mouse down event; 2) any raw key down
+  // event; and 3) any gesture tap event (which includes taps and scrolls).

[nasko, 2015/10/28 17:36:12]

If this is again doing extra work during scrolling, perf should be considered. I
would suggest discussing this with nduca@ or someone else more versed in perf
than myself.

[dominickn, 2015/10/29 00:03:19]

GestureTapDown fires once at the beginning of a scroll, but no more times after
that while the user is scrolling until they tap again on the screen. This is in
contrast to MouseWheel, which continually fires while scrolling. There's no
additional load during scrolling. 

[nasko, 2015/10/29 00:07:26]

Awesome! Thanks for the context.

+  virtual void OnUserInteraction(const blink::WebInputEvent::Type type);
+
   // Routines used to send the RenderWidget its screen color profile.
   void DispatchColorProfile();
   void SendColorProfile();