Makes tile-creation lazy

cc/layers/picture_layer_impl.h

Index: cc/layers/picture_layer_impl.h
diff --git a/cc/layers/picture_layer_impl.h b/cc/layers/picture_layer_impl.h
index d10b93f9af0f2e55778dbb9da529732b8273ff6b..925187c6e6750a7053817d5f4e00e8bd90754281 100644
--- a/cc/layers/picture_layer_impl.h
+++ b/cc/layers/picture_layer_impl.h
@@ -46,11 +46,14 @@ class CC_EXPORT PictureLayerImpl : public LayerImpl,
 
   // 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();