Fix mouse wheel over-scrolls when display is scaled and scroll is paginated

third_party/WebKit/public/web/WebViewClient.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 253 matching lines @@
   // WebWidgetClient overrides.
   void closeWidgetSoon() override {}
   void convertViewportToWindow(WebRect* rect) override {}
   void convertWindowToViewport(WebFloatRect* rect) override {}
   void didHandleGestureEvent(const WebGestureEvent& event,
                              bool eventCancelled) override {}
   void didOverscroll(const WebFloatSize& overscrollDelta,
                      const WebFloatSize& accumulatedOverscroll,
                      const WebFloatPoint& positionInViewport,
                      const WebFloatSize& velocityInViewport) override {}
+  float GetOriginalDeviceScaleFactor() const override { return 1.0f; }

[chengx, 2017/01/06 23:46:36]

Bret:
Be careful adding functions to the public interfaces. I don't think Blink should
have access to the device scale factor directly.

   void hasTouchEventHandlers(bool) override {}
   void initializeLayerTreeView() override {}
   void resetInputMethod() override {}
   WebScreenInfo screenInfo() override { return WebScreenInfo(); }
   void setTouchAction(WebTouchAction touchAction) override {}
   void showImeIfNeeded() override {}
   void showUnhandledTapUIIfNeeded(const WebPoint& tappedPosition,
                                   const WebNode& tappedNode,
                                   bool pageChanged) override {}
   void show(WebNavigationPolicy) override {}
   virtual WebWidgetClient* widgetClient() { return this; }
 
  protected:
   ~WebViewClient() {}
 };
 
 }  // namespace blink
 
 #endif