Implement windows mousewheel scroll by page functionality

cc/input/input_handler.h

 // Copyright 2011 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 CC_INPUT_INPUT_HANDLER_H_
 #define CC_INPUT_INPUT_HANDLER_H_
 
 #include "base/basictypes.h"
 #include "base/time.h"
 #include "cc/base/cc_export.h"
+#include "third_party/WebKit/Source/Platform/chromium/public/WebScrollbar.h"
 
 namespace gfx {
 class Point;
 class PointF;
 class Vector2d;
 class Vector2dF;
 }
 
 namespace cc {
 
@@ skipping 23 matching lines @@
   // should be in viewport (logical pixel) coordinates. Otherwise they are in
   // scrolling layer's (logical pixel) space. If there is no room to move the
   // layer in the requested direction, its first ancestor layer that can be
   // scrolled will be moved instead. If no layer can be moved in the requested
   // direction at all, then false is returned. If any layer is moved, then
   // true is returned.
   // Should only be called if ScrollBegin() returned ScrollStarted.
   virtual bool ScrollBy(gfx::Point viewport_point,
                         gfx::Vector2dF scroll_delta) = 0;
 
+  virtual bool ScrollVerticallyByPage(
+      gfx::Point viewport_point,
+      WebKit::WebScrollbar::ScrollDirection direction) = 0;
+
   // Stop scrolling the selected layer. Should only be called if ScrollBegin()
   // returned ScrollStarted.
   virtual void ScrollEnd() = 0;
 
   virtual void PinchGestureBegin() = 0;
   virtual void PinchGestureUpdate(float magnify_delta, gfx::Point anchor) = 0;
   virtual void PinchGestureEnd() = 0;
 
   virtual void StartPageScaleAnimation(gfx::Vector2d target_offset,
                                        bool anchor_point,
@@ skipping 25 matching lines @@
  protected:
   InputHandler() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InputHandler);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_INPUT_HANDLER_H_