Implement desktop compatibility viewport

cc/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_LAYER_TREE_IMPL_H_
 #define CC_LAYER_TREE_IMPL_H_
 
 #include "base/hash_tables.h"
 #include "cc/layer_impl.h"
 
@@ skipping 84 matching lines @@
   LayerImpl* RootScrollLayer();
   LayerImpl* CurrentlyScrollingLayer();
   void set_currently_scrolling_layer(LayerImpl* layer) {
     currently_scrolling_layer_ = layer;
   }
 
   void ClearCurrentlyScrollingLayer();
 
   void FindRootScrollLayer();
   void UpdateMaxScrollOffset();
+  void UpdateFixedPositionViewport();
 
   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 51 matching lines @@
   LayerList render_surface_layer_list_;
 
   bool contents_textures_purged_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }
 
 #endif  // CC_LAYER_TREE_IMPL_H_