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

content/renderer/render_thread_impl.h

Index: content/renderer/render_thread_impl.h
diff --git a/content/renderer/render_thread_impl.h b/content/renderer/render_thread_impl.h
index 50d1362f43155b11d08332cbd65a86dc3d468098..127c687d747abbe3ff247e53f1499555bdde3eb4 100644
--- a/content/renderer/render_thread_impl.h
+++ b/content/renderer/render_thread_impl.h
@@ -257,6 +257,11 @@ class CONTENT_EXPORT RenderThreadImpl : public RenderThread,
   // on the renderer's main thread.
   scoped_refptr<base::MessageLoopProxy> GetFileThreadMessageLoopProxy();
 
+  // Returns a MessageLoopProxy instance corresponding to the message loop
+  // of the thread on which media operations should be run. Must be called
+  // on the renderer's main thread.
+  scoped_refptr<base::MessageLoopProxy> GetMediaThreadMessageLoopProxy();
+
   // Causes the idle handler to skip sending idle notifications
   // on the two next scheduled calls, so idle notifications are
   // not sent for at least one notification delay.
@@ -425,6 +430,9 @@ class CONTENT_EXPORT RenderThreadImpl : public RenderThread,
   // May be null if overridden by ContentRendererClient.
   scoped_ptr<base::Thread> compositor_thread_;
 
+  // Thread for running multimedia operations (e.g., video decoding).
+  scoped_ptr<base::Thread> media_thread_;
+
   // Will point to appropriate MessageLoopProxy after initialization,
   // regardless of whether |compositor_thread_| is overriden.
   scoped_refptr<base::MessageLoopProxy> compositor_message_loop_proxy_;