Support single-threaded impl-side painting

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 450b2721bc9c1f4b6662e3706f624bedf3968797..59e12757733db5308c23719e88f7a5bf5fd3e667 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -483,6 +483,9 @@ class CC_EXPORT LayerTreeHostImpl
   void ResetRequiresHighResToDraw() { requires_high_res_to_draw_ = false; }
   bool RequiresHighResToDraw() const { return requires_high_res_to_draw_; }
 
+  // Only valid for synchronous (non-scheduled) single-threaded case.
+  void SynchronouslyInitializeAllTiles();
+
  protected:
   LayerTreeHostImpl(
       const LayerTreeSettings& settings,
@@ -694,6 +697,7 @@ class CC_EXPORT LayerTreeHostImpl
 
   RenderingStatsInstrumentation* rendering_stats_instrumentation_;
   MicroBenchmarkControllerImpl micro_benchmark_controller_;
+  scoped_ptr<TaskGraphRunner> single_thread_synchronous_task_graph_runner_;

[reveman, 2014/10/28 03:46:33]

TaskGraphRunner is pretty lightweight. I think you can remove scoped_ptr<> and
make the code in the .cc file a bit cleaner by removing the possibility for this
to not be initialized. 

 
   bool need_to_update_visible_tiles_before_draw_;