Don't crash when a context can't be created for HW video decode.

content/renderer/render_thread_impl.cc

 // Copyright (c) 2012 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 "content/renderer/render_thread_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <vector>
@@ skipping 754 matching lines @@
     } else {
       gpu_vda_context3d_.reset();
     }
   }
   if (!gpu_vda_context3d_.get()) {
     gpu_vda_context3d_.reset(
         WebGraphicsContext3DCommandBufferImpl::CreateOffscreenContext(
             this, WebKit::WebGraphicsContext3D::Attributes(),
             GURL("chrome://gpu/RenderThreadImpl::GetGpuVDAContext3D")));
   }
+  if (!gpu_vda_context3d_.get())
+    return base::WeakPtr<WebGraphicsContext3DCommandBufferImpl>();
   return gpu_vda_context3d_->AsWeakPtr();
 }
 
 content::AudioRendererMixerManager*
 RenderThreadImpl::GetAudioRendererMixerManager() {
   if (!audio_renderer_mixer_manager_.get()) {
     audio_renderer_mixer_manager_.reset(new AudioRendererMixerManager(
         audio_hardware::GetOutputSampleRate(),
         audio_hardware::GetOutputBufferSize()));
   }
@@ skipping 277 matching lines @@
 
 scoped_refptr<base::MessageLoopProxy>
 RenderThreadImpl::GetFileThreadMessageLoopProxy() {
   DCHECK(message_loop() == MessageLoop::current());
   if (!file_thread_.get()) {
     file_thread_.reset(new base::Thread("Renderer::FILE"));
     file_thread_->Start();
   }
   return file_thread_->message_loop_proxy();
 }