Add viewport scrollbar class to support overlay scrollbars for pinch zoom virtual viewport.

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 <string>
 #include <vector>
 
@@ skipping 92 matching lines @@
   }
 
   LayerImpl* RootScrollLayer() const;
   LayerImpl* RootClipLayer() const;
   LayerImpl* CurrentlyScrollingLayer() const;
   void SetCurrentlyScrollingLayer(LayerImpl* layer);
   void ClearCurrentlyScrollingLayer();
 
   void FindRootScrollLayer();
   void UpdateMaxScrollOffset();
+  void SetPinchViewportLayerIds(int page_scale_layer_id,
+                                int inner_viewport_scroll_layer_id,
+                                int outer_viewport_scroll_layer_id);
 
   SkColor background_color() const { return background_color_; }
   void set_background_color(SkColor color) { background_color_ = color; }
 
   bool has_transparent_background() const {
     return has_transparent_background_;
   }
   void set_has_transparent_background(bool transparent) {
     has_transparent_background_ = transparent;
   }
@@ skipping 80 matching lines @@
   LayerTreeHostImpl* layer_tree_host_impl_;
   int source_frame_number_;
   scoped_ptr<LayerImpl> root_layer_;
   HeadsUpDisplayLayerImpl* hud_layer_;
   LayerImpl* root_scroll_layer_;
   LayerImpl* currently_scrolling_layer_;
   LayerScrollOffsetDelegate* root_layer_scroll_offset_delegate_;
   SkColor background_color_;
   bool has_transparent_background_;
 
+  LayerImpl* page_scale_layer_;
+  LayerImpl* inner_viewport_scroll_layer_;
+  LayerImpl* outer_viewport_scroll_layer_;
+
   float page_scale_factor_;
   float page_scale_delta_;
   float sent_page_scale_delta_;
   float min_page_scale_factor_;
   float max_page_scale_factor_;
 
   typedef base::hash_map<int, LayerImpl*> LayerIdMap;
   LayerIdMap layer_id_map_;
 
   // Persisted state for non-impl-side-painting.
@@ skipping 12 matching lines @@
   bool needs_full_tree_sync_;
 
   ui::LatencyInfo latency_info_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_