Implement on demand quad rasterization for PicturePiles.

cc/tile_draw_quad.h

Index: cc/tile_draw_quad.h
diff --git a/cc/tile_draw_quad.h b/cc/tile_draw_quad.h
index ff04b4bcbb60f2b651f5161ace97950961e35a1e..6c09ccd0a96eb3775c7fc79d6ec978fb5c5f2499 100644
--- a/cc/tile_draw_quad.h
+++ b/cc/tile_draw_quad.h
@@ -41,11 +41,16 @@ class CC_EXPORT TileDrawQuad : public DrawQuad {
   gfx::Size texture_size;
   bool swizzle_contents;
 
+  virtual bool IsPictureQuad() const;
+
   virtual void IterateResources(const ResourceIteratorCallback& callback)
       OVERRIDE;
 
   static const TileDrawQuad* MaterialCast(const DrawQuad*);
- private:
+
+ protected:
+  virtual DrawQuad::Material material() const;
+
   TileDrawQuad();
 };