Disable overscroll navigation when emulating touch.

content/browser/renderer_host/render_widget_host_delegate.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_RENDER_WIDGET_HOST_DELEGATE_H_
 #define CONTENT_BROWSER_RENDER_WIDGET_HOST_DELEGATE_H_
 
 #include "build/build_config.h"
 #include "content/common/content_export.h"
 #include "ui/gfx/native_widget_types.h"
@@ skipping 41 matching lines @@
   // Returns true if the |event| was handled.
   virtual bool PreHandleGestureEvent(const blink::WebGestureEvent& event);
 
   // Callback to inform the browser that the renderer did not process the
   // specified gesture event.  Returns true if the |event| was handled.
   virtual bool HandleGestureEvent(const blink::WebGestureEvent& event);
 
   // Notifies that screen rects were sent to renderer process.
   virtual void DidSendScreenRects(RenderWidgetHostImpl* rwh) {}
 
+  // Notifies that overscrolling content should be disabled.
+  virtual void SetOverscrollContentDisabled(bool disabled) {}

[mfomitchev, 2014/06/04 21:50:36]

This doesn't really belong in the RWHDelegate interface IMHO since RWH knows
nothing about overscroll. Perhaps it would make sense to handle
ViewHostMsg_SetTouchEventEmulationEnabled in web_contents_impl instead? Then we
wouldn't have to change the delegate interface (although we may need to make the
method for enabling touch emulation in RWHI public). 

[dgozman, 2014/06/06 14:07:31]

I don't like this one either. Unfortunately, moving message handling to
WebContents is hard, since during navigation it has multiple RWHIs and
complicated logic. Ensuring the right time for this message initiated from Blink
may be unfeasible.

We should either go from RWHI to WebContents (as in this patch), or disable
overscroll on RWHV/OverscrollController level. WDYT?

[Avi (use Gerrit), 2014/06/06 14:36:17]

Well, RWH knows about "touch emulation" so perhaps this could be renamed as
OnSetTouchEventEmulationEnabled, and let the WebContents say, "hey, in this case
let's disable overscroll".

[mfomitchev, 2014/06/06 15:32:48]

This sounds reasonable to me.

[dgozman, 2014/06/06 15:45:28]

Done.

+
 #if defined(OS_WIN)
   // Returns the widget's parent's NativeViewAccessible.
   virtual gfx::NativeViewAccessible GetParentNativeViewAccessible();
 #endif
 
  protected:
   virtual ~RenderWidgetHostDelegate() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDER_WIDGET_HOST_DELEGATE_H_