Makes tile-creation lazy

cc/layers/picture_layer_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_LAYERS_PICTURE_LAYER_IMPL_H_
 #define CC_LAYERS_PICTURE_LAYER_IMPL_H_
 
 #include "cc/base/scoped_ptr_vector.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/resources/picture_layer_tiling.h"
@@ skipping 28 matching lines @@
   virtual void DidLoseOutputSurface() OVERRIDE;
   virtual void CalculateContentsScale(float ideal_contents_scale,
                                       bool animating_transform_to_screen,
                                       float* contents_scale_x,
                                       float* contents_scale_y,
                                       gfx::Size* content_bounds) OVERRIDE;
   virtual skia::RefPtr<SkPicture> GetPicture() OVERRIDE;
 
   // PictureLayerTilingClient overrides.
   virtual scoped_refptr<Tile> CreateTile(PictureLayerTiling* tiling,
-                                         gfx::Rect content_rect) OVERRIDE;
+                                         const gfx::Rect& content_rect,
+                                         const gfx::Rect& paint_rect) OVERRIDE;
   virtual void UpdatePile(Tile* tile) OVERRIDE;
   virtual gfx::Size CalculateTileSize(
       gfx::Size current_tile_size,
       gfx::Size content_bounds) OVERRIDE;
+  virtual const Region* GetInvalidation() OVERRIDE;
+  virtual const PictureLayerTiling* GetSibling(const PictureLayerTiling* tiling) OVERRIDE;

[enne (OOO), 2013/03/27 16:16:27]

naming bikeshed: GetSibling => GetTwinTiling

Layers are siblings when they have the same parent and are in the same tree. 
We've been calling layers "twins" if they have the same layer id but exist in a
different tree.  These tilings are from "layer twins", so I think it'd be more
clear to call them twin tilings.

 
   // PushPropertiesTo active tree => pending tree
   void SyncFromActiveLayer();
   void SyncTiling(
       const PictureLayerTiling* tiling,
       const Region& pending_layer_invalidation);
 
   void CreateTilingSet();
   void TransferTilingSet(scoped_ptr<PictureLayerTilingSet> tilings);
 
@@ skipping 43 matching lines @@
   float raster_source_scale_;
   bool raster_source_scale_was_animating_;
 
   friend class PictureLayer;
   DISALLOW_COPY_AND_ASSIGN(PictureLayerImpl);
 };
 
 }
 
 #endif  // CC_LAYERS_PICTURE_LAYER_IMPL_H_