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 8e440869460638cf468f85281a7ef34749504b10..14388832e873070661c0ad4038298ac3e5442a99 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1327,6 +1327,16 @@ 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) {