Move viewport scrolling logic into separate class

cc/trees/layer_tree_impl.h

 // Copyright 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 CC_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 26 matching lines @@
 class LayerTreeSettings;
 class MemoryHistory;
 class OutputSurface;
 class PageScaleAnimation;
 class PaintTimeCounter;
 class PictureLayerImpl;
 class Proxy;
 class ResourceProvider;
 class TileManager;
 class UIResourceRequest;
+class Viewport;
 struct PendingPageScaleAnimation;
 struct RendererCapabilities;
 struct SelectionHandle;
 
 typedef std::vector<UIResourceRequest> UIResourceRequestQueue;
 typedef SyncedProperty<AdditionGroup<float>> SyncedTopControls;
 typedef SyncedProperty<AdditionGroup<gfx::Vector2dF>> SyncedElasticOverscroll;
 
 class CC_EXPORT LayerTreeImpl {
  public:
@@ skipping 265 matching lines @@
     return top_controls_shown_ratio_->Current(IsActiveTree());
   }
   void set_top_controls_height(float top_controls_height);
   float top_controls_height() const { return top_controls_height_; }
   void PushTopControlsFromMainThread(float top_controls_shown_ratio);
 
   void SetPendingPageScaleAnimation(
       scoped_ptr<PendingPageScaleAnimation> pending_animation);
   scoped_ptr<PendingPageScaleAnimation> TakePendingPageScaleAnimation();
 
+  Viewport* viewport() { return viewport_.get(); }
+
  protected:
   explicit LayerTreeImpl(
       LayerTreeHostImpl* layer_tree_host_impl,
       scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
       scoped_refptr<SyncedTopControls> top_controls_shown_ratio,
       scoped_refptr<SyncedElasticOverscroll> elastic_overscroll);
   float ClampPageScaleFactorToLimits(float page_scale_factor) const;
   void PushPageScaleFactorAndLimits(const float* page_scale_factor,
                                     float min_page_scale_factor,
                                     float max_page_scale_factor);
@@ skipping 67 matching lines @@
   bool top_controls_shrink_blink_size_;
 
   float top_controls_height_;
 
   // The amount that the top controls are shown from 0 (hidden) to 1 (fully
   // shown).
   scoped_refptr<SyncedTopControls> top_controls_shown_ratio_;
 
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
+  scoped_ptr<Viewport> viewport_;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_