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

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 0f86870fba07207c47a15003c8884158e750c6e3..ed8cbd2522c2f16fa82731c35ddc36ba6884f5bc 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1330,6 +1330,16 @@ RenderThreadImpl::GetFileThreadMessageLoopProxy() {
   return file_thread_->message_loop_proxy();
 }
 
+scoped_refptr<base::MessageLoopProxy>
+RenderThreadImpl::GetMediaThreadMessageLoopProxy() {
+  DCHECK(message_loop() == base::MessageLoop::current());
+  if (!media_thread_) {
+    media_thread_.reset(new base::Thread("Media"));
+    media_thread_->Start();
+  }
+  return media_thread_->message_loop_proxy();
+}
+
 void RenderThreadImpl::SetFlingCurveParameters(
     const std::vector<float>& new_touchpad,
     const std::vector<float>& new_touchscreen) {