Support single-threaded impl-side painting

cc/trees/layer_tree_host_impl.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 465 matching lines @@
 
   void GetPictureLayerImplPairs(
       std::vector<PictureLayerImpl::Pair>* layers) const;
 
   void SetTopControlsLayoutHeight(float height);
 
   void SetRequiresHighResToDraw() { requires_high_res_to_draw_ = true; }
   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,
       LayerTreeHostImplClient* client,
       Proxy* proxy,
       RenderingStatsInstrumentation* rendering_stats_instrumentation,
       SharedBitmapManager* shared_bitmap_manager,
       GpuMemoryBufferManager* gpu_memory_buffer_manager,
       int id);
 
@@ skipping 191 matching lines @@
 
   BeginFrameArgs current_begin_frame_args_;
 
   // Expected time between two begin impl frame calls.
   base::TimeDelta begin_impl_frame_interval_;
 
   scoped_ptr<AnimationRegistrar> animation_registrar_;
 
   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_;
 
   // Optional callback to notify of new tree activations.
   base::Closure tree_activation_callback_;
 
   SharedBitmapManager* shared_bitmap_manager_;
   GpuMemoryBufferManager* gpu_memory_buffer_manager_;
   int id_;
 
   std::set<SwapPromiseMonitor*> swap_promise_monitor_;
 
   std::vector<PictureLayerImpl*> picture_layers_;
   std::vector<PictureLayerImpl::Pair> picture_layer_pairs_;
 
   bool requires_high_res_to_draw_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_