Reland: Use a shared thread for media operations (round 3).

content/test/layouttest_support.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/public/test/layouttest_support.h"
 
 #include "base/callback.h"
 #include "base/lazy_instance.h"
 #include "content/common/gpu/image_transport_surface.h"
 #include "content/renderer/render_thread_impl.h"
@@ skipping 93 matching lines @@
                           const WebSize& max_size) {
   static_cast<RenderViewImpl*>(render_view)
       ->EnableAutoResizeForTesting(min_size, max_size);
 }
 
 void DisableAutoResizeMode(RenderView* render_view, const WebSize& new_size) {
   static_cast<RenderViewImpl*>(render_view)
       ->DisableAutoResizeForTesting(new_size);
 }
 
+scoped_refptr<base::MessageLoopProxy> GetMediaThreadMessageLoopProxy() {
+  return RenderThreadImpl::current()->GetMediaThreadMessageLoopProxy();
+}
+
 }  // namespace content