Notify WebContentsObservers of user interactions.

content/browser/renderer_host/render_widget_host_impl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 
 #include <list>
 #include <map>
 #include <string>
@@ skipping 560 matching lines @@
 
   // Called by |new_content_rendering_timeout_| if a renderer has loaded new
   // content but failed to produce a compositor frame in a defined time.
   void ClearDisplayedGraphics();
 
   // Called if we know the renderer is responsive. When we currently think the
   // renderer is unresponsive, this will clear that state and call
   // 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();
 
   // IPC message handlers
   void OnRenderProcessGone(int status, int error_code);
   void OnClose();
   void OnUpdateScreenRectsAck();
   void OnRequestMove(const gfx::Rect& pos);
   void OnSetTooltipText(const base::string16& tooltip_text,
@@ skipping 253 matching lines @@
   base::TimeDelta new_content_rendering_delay_;
 
   base::WeakPtrFactory<RenderWidgetHostImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_