cc: Only allow trees created at the current viewport size to draw.

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 161 matching lines @@
   AnimationRegistrar* animationRegistrar() const;
 
   void PushPersistedState(LayerTreeImpl* pendingTree);
 
   void DidBecomeActive();
 
   bool ContentsTexturesPurged() const;
   void SetContentsTexturesPurged();
   void ResetContentsTexturesPurged();
 
+  // Set on the active tree when the viewport size recently changed
+  // and the active tree's size is now out of date.
+  bool ViewportSizeInvalid() const;
+  void SetViewportSizeInvalid();
+  void ResetViewportSizeInvalid();
+
   // Useful for debug assertions, probably shouldn't be used for anything else.
   Proxy* proxy() const;
 
 protected:
   LayerTreeImpl(LayerTreeHostImpl* layer_tree_host_impl);
 
   LayerTreeHostImpl* layer_tree_host_impl_;
   int source_frame_number_;
   scoped_ptr<LayerImpl> root_layer_;
   HeadsUpDisplayLayerImpl* hud_layer_;
@@ skipping 12 matching lines @@
   LayerIdMap layer_id_map_;
 
   // Persisted state for non-impl-side-painting.
   int scrolling_layer_id_from_previous_tree_;
 
   // List of visible layers for the most recently prepared frame. Used for
   // rendering and input event hit testing.
   LayerList render_surface_layer_list_;
 
   bool contents_textures_purged_;
+  bool viewport_size_invalid_;
   bool needs_update_draw_properties_;
 
   // In impl-side painting mode, this is true when the tree may contain
   // structural differences relative to the active tree.
   bool needs_full_tree_sync_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }
 
 #endif  // CC_LAYER_TREE_IMPL_H_