cc: Add null checks for GrContext created by ContextProviderCommandBuffer.

cc/trees/layer_tree_host_impl_unittest.cc

 // 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.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/bind.h"
@@ skipping 5913 matching lines @@
   EXPECT_EQ(nothing_cutoff_value, current_priority_cutoff_value_);
 
   host_impl_->SetVisible(true);
   EXPECT_EQ(policy1.bytes_limit_when_visible, current_limit_bytes_);
   EXPECT_EQ(everything_cutoff_value, current_priority_cutoff_value_);
 
   // Now enable GPU rasterization and test if we get nice to have cutoff,
   // when visible.
   LayerTreeSettings settings;
   settings.gpu_rasterization_enabled = true;
-  host_impl_ = LayerTreeHostImpl::Create(
-      settings, this, &proxy_, &stats_instrumentation_, NULL, NULL, NULL, 0);
+  CreateHostImpl(settings, CreateOutputSurface());
   host_impl_->set_content_is_suitable_for_gpu_rasterization(true);
   host_impl_->set_has_gpu_rasterization_trigger(true);
   host_impl_->UpdateGpuRasterizationStatus();
   host_impl_->SetVisible(true);
   host_impl_->SetMemoryPolicy(policy1);
   EXPECT_EQ(policy1.bytes_limit_when_visible, current_limit_bytes_);
   EXPECT_EQ(allow_nice_to_have_cutoff_value, current_priority_cutoff_value_);
 
   host_impl_->SetVisible(false);
   EXPECT_EQ(0u, current_limit_bytes_);
@@ skipping 1834 matching lines @@
   host_impl_->set_has_gpu_rasterization_trigger(false);
   host_impl_->set_content_is_suitable_for_gpu_rasterization(false);
   host_impl_->UpdateGpuRasterizationStatus();
   EXPECT_EQ(GpuRasterizationStatus::ON_FORCED,
             host_impl_->gpu_rasterization_status());
   EXPECT_TRUE(host_impl_->use_gpu_rasterization());
 }
 
 }  // namespace
 }  // namespace cc