cc: GPU rasterize tiles synchronously in PrepareToDraw

cc/resources/rasterizer.h

Index: cc/resources/rasterizer.h
diff --git a/cc/resources/rasterizer.h b/cc/resources/rasterizer.h
index db84c2223eba9566a2b7e5218b3bef8762cceafe..04249b79b99dcaa23388ed90a338eb35104a257f 100644
--- a/cc/resources/rasterizer.h
+++ b/cc/resources/rasterizer.h
@@ -149,6 +149,9 @@ class CC_EXPORT Rasterizer {
   // CheckForCompletedTasks() is called.
   virtual void Shutdown() = 0;
 
+  // Run all raster tasks in |queue| synchronously.
+  virtual void RunTasks(RasterTaskQueue* queue) = 0;
+
   // Schedule running of raster tasks in |queue| and all dependencies.
   // Previously scheduled tasks that are not in |queue| will be canceled unless
   // already running. Once scheduled, reply callbacks are guaranteed to run for