Use enum instead of string in MessageLoopFactory::GetMessageLoop*

media/filters/gpu_video_decoder.h

Index: media/filters/gpu_video_decoder.h
diff --git a/media/filters/gpu_video_decoder.h b/media/filters/gpu_video_decoder.h
index df765e6420d2627c767ff007de357c122eea4ad1..576cc6969f1cbedfe1a45e5c3010ea9ecad0e57c 100644
--- a/media/filters/gpu_video_decoder.h
+++ b/media/filters/gpu_video_decoder.h
@@ -56,8 +56,9 @@ class MEDIA_EXPORT GpuVideoDecoder
     virtual ~Factories();
   };
 
-  GpuVideoDecoder(MessageLoop* message_loop,
-                  MessageLoop* vda_loop,
+  typedef base::Callback<scoped_refptr<base::MessageLoopProxy>()> MessageLoopCB;
+  GpuVideoDecoder(const MessageLoopCB& message_loop_cb,
+                  const scoped_refptr<base::MessageLoopProxy>& vda_loop_proxy,
                   const scoped_refptr<Factories>& factories);
 
   // VideoDecoder implementation.
@@ -149,6 +150,9 @@ class MEDIA_EXPORT GpuVideoDecoder
   // Pointer to the demuxer stream that will feed us compressed buffers.
   scoped_refptr<DemuxerStream> demuxer_stream_;
 
+  // This is !is_null() iff Initialize() hasn't been called.
+  MessageLoopCB message_loop_factory_cb_;
+
   // MessageLoop on which to fire callbacks and trampoline calls to this class
   // if they arrive on other loops.
   scoped_refptr<base::MessageLoopProxy> gvd_loop_proxy_;