Implement one-page-at-a-time mousewheel scrolling in the impl thread.

cc/layer.h

 // Copyright 2010 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_LAYER_H_
 #define CC_LAYER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 137 matching lines @@
     Layer* renderTarget() { DCHECK(!m_drawProperties.render_target || m_drawProperties.render_target->renderSurface()); return m_drawProperties.render_target; }
     const Layer* renderTarget() const { DCHECK(!m_drawProperties.render_target || m_drawProperties.render_target->renderSurface()); return m_drawProperties.render_target; }
     RenderSurface* renderSurface() const { return m_drawProperties.render_surface.get(); }
 
     void setScrollOffset(gfx::Vector2d);
     gfx::Vector2d scrollOffset() const { return m_scrollOffset; }
 
     void setMaxScrollOffset(gfx::Vector2d);
     gfx::Vector2d maxScrollOffset() const { return m_maxScrollOffset; }
 
+    void setVisibleScrollArea(gfx::Size);
+    gfx::Size visibleScrollArea() const { return m_visibleScrollArea; }
+
     void setScrollable(bool);
     bool scrollable() const { return m_scrollable; }
 
     void setShouldScrollOnMainThread(bool);
     bool shouldScrollOnMainThread() const { return m_shouldScrollOnMainThread; }
 
     void setHaveWheelEventHandlers(bool);
     bool haveWheelEventHandlers() const { return m_haveWheelEventHandlers; }
 
     void setNonFastScrollableRegion(const Region&);
@@ skipping 183 matching lines @@
 
     ObserverList<LayerAnimationEventObserver> m_layerAnimationObservers;
 
     scoped_refptr<LayerAnimationController> m_layerAnimationController;
 
     // Layer properties.
     gfx::Size m_bounds;
 
     gfx::Vector2d m_scrollOffset;
     gfx::Vector2d m_maxScrollOffset;
+    gfx::Size m_visibleScrollArea;
     bool m_scrollable;
     bool m_shouldScrollOnMainThread;
     bool m_haveWheelEventHandlers;
     Region m_nonFastScrollableRegion;
     Region m_touchEventHandlerRegion;
     gfx::PointF m_position;
     gfx::PointF m_anchorPoint;
     SkColor m_backgroundColor;
     std::string m_debugName;
     float m_opacity;
@@ skipping 29 matching lines @@
     WebKit::WebLayerScrollClient* m_layerScrollClient;
 
     DrawProperties<Layer, RenderSurface> m_drawProperties;
 };
 
 void sortLayers(std::vector<scoped_refptr<Layer> >::iterator, std::vector<scoped_refptr<Layer> >::iterator, void*);
 
 }  // namespace cc
 
 #endif  // CC_LAYER_H_