cc: Add null checks for GrContext created by ContextProviderCommandBuffer.

cc/resources/scoped_gpu_raster.cc

 // Copyright 2014 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.
 
 #include "cc/resources/scoped_gpu_raster.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
 #include "third_party/khronos/GLES2/gl2.h"
 #include "third_party/khronos/GLES2/gl2ext.h"
 #include "third_party/skia/include/gpu/GrContext.h"
 
@@ skipping 12 matching lines @@
 
 void ScopedGpuRaster::BeginGpuRaster() {
   GLES2Interface* gl = context_provider_->ContextGL();
 
   // TODO(alokp): Use a trace macro to push/pop markers.
   // Using push/pop functions directly incurs cost to evaluate function
   // arguments even when tracing is disabled.
   gl->PushGroupMarkerEXT(0, "GpuRasterization");
 
   class GrContext* gr_context = context_provider_->GrContext();
-  gr_context->resetContext();
+  if (gr_context)
+    gr_context->resetContext();
 }
 
 void ScopedGpuRaster::EndGpuRaster() {
   class GrContext* gr_context = context_provider_->GrContext();
-  gr_context->flush();
+  if (gr_context)
+    gr_context->flush();
 
   GLES2Interface* gl = context_provider_->ContextGL();
 
   // Restore default GL unpack alignment.  TextureUploader expects this.
   gl->PixelStorei(GL_UNPACK_ALIGNMENT, 4);
 
   // TODO(alokp): Use a trace macro to push/pop markers.
   // Using push/pop functions directly incurs cost to evaluate function
   // arguments even when tracing is disabled.
   gl->PopGroupMarkerEXT();
 }
 
 }  // namespace cc