cc: GPU rasterize tiles synchronously in PrepareToDraw.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 54a16aa819d946c0c28f5545452285a0913cee22..efcf9f4f84bcd339ac504ecbaf6b8b2421d46806 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -52,6 +52,9 @@ class PaintTimeCounter;
 class PictureLayerImpl;
 class RasterTilePriorityQueue;
 class TileTaskWorkerPool;
+class Rasterizer;
+class SoftwareRasterizer;
+class GpuRasterizer;
 class RenderPassDrawQuad;
 class RenderingStatsInstrumentation;
 class ResourcePool;
@@ -200,6 +203,7 @@ class CC_EXPORT LayerTreeHostImpl
   void DidAnimateScrollOffset();
   void SetViewportDamage(const gfx::Rect& damage_rect);
 
+  virtual void PrepareTilesBeforeDraw();
   virtual void PrepareTiles();
 
   // Returns DRAW_SUCCESS unless problems occured preparing the frame, and we
@@ -501,6 +505,7 @@ class CC_EXPORT LayerTreeHostImpl
 
   virtual void CreateResourceAndTileTaskWorkerPool(
       scoped_ptr<TileTaskWorkerPool>* tile_task_worker_pool,
+      scoped_ptr<Rasterizer>* rasterizer,
       scoped_ptr<ResourcePool>* resource_pool,
       scoped_ptr<ResourcePool>* staging_resource_pool);
 
@@ -611,6 +616,7 @@ class CC_EXPORT LayerTreeHostImpl
   bool use_gpu_rasterization_;
   GpuRasterizationStatus gpu_rasterization_status_;
   scoped_ptr<TileTaskWorkerPool> tile_task_worker_pool_;
+  scoped_ptr<Rasterizer> rasterizer_;
   scoped_ptr<ResourcePool> resource_pool_;
   scoped_ptr<ResourcePool> staging_resource_pool_;
   scoped_ptr<Renderer> renderer_;