cc: Add null checks for GrContext created by ContextProviderCommandBuffer.

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 <set>
 #include <string>
 #include <vector>
@@ skipping 309 matching lines @@
 
   virtual bool InitializeRenderer(scoped_ptr<OutputSurface> output_surface);
   TileManager* tile_manager() { return tile_manager_.get(); }
 
   void set_has_gpu_rasterization_trigger(bool flag) {
     has_gpu_rasterization_trigger_ = flag;
   }
   void set_content_is_suitable_for_gpu_rasterization(bool flag) {
     content_is_suitable_for_gpu_rasterization_ = flag;
   }
+  bool CanUseGpuRasterization();
   void UpdateGpuRasterizationStatus();
   bool use_gpu_rasterization() const { return use_gpu_rasterization_; }
   bool use_msaa() const { return use_msaa_; }
 
   GpuRasterizationStatus gpu_rasterization_status() const {
     return gpu_rasterization_status_;
   }
 
   bool create_low_res_tiling() const {
     return settings_.create_low_res_tiling && !use_gpu_rasterization_;
@@ skipping 420 matching lines @@
   scoped_ptr<FrameTimingTracker> frame_timing_tracker_;
 
   scoped_ptr<Viewport> viewport_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_