Use enum instead of string in MessageLoopFactory::GetMessageLoop*

media/filters/ffmpeg_audio_decoder.h

Index: media/filters/ffmpeg_audio_decoder.h
diff --git a/media/filters/ffmpeg_audio_decoder.h b/media/filters/ffmpeg_audio_decoder.h
index c63edaed5ef76a1bccb8cf14a67cdd512bad893f..8e67f59c72c2dff6aec55b82d50f68f6d6517110 100644
--- a/media/filters/ffmpeg_audio_decoder.h
+++ b/media/filters/ffmpeg_audio_decoder.h
@@ -8,13 +8,16 @@
 #include <list>
 
 #include "base/callback.h"
-#include "base/message_loop.h"
 #include "media/base/audio_decoder.h"
 #include "media/base/demuxer_stream.h"
 
 struct AVCodecContext;
 struct AVFrame;
 
+namespace base {
+class MessageLoopProxy;
+}
+
 namespace media {
 
 class DataBuffer;
@@ -22,7 +25,10 @@ class DecoderBuffer;
 
 class MEDIA_EXPORT FFmpegAudioDecoder : public AudioDecoder {
  public:
-  FFmpegAudioDecoder(const base::Callback<MessageLoop*()>& message_loop_cb);
+  typedef base::Callback<
+      scoped_refptr<base::MessageLoopProxy>()> MessageLoopFactoryCB;
+  explicit FFmpegAudioDecoder(
+      const MessageLoopFactoryCB& message_loop_factory_cb);
 
   // AudioDecoder implementation.
   virtual void Initialize(const scoped_refptr<DemuxerStream>& stream,
@@ -58,8 +64,9 @@ class MEDIA_EXPORT FFmpegAudioDecoder : public AudioDecoder {
   base::TimeDelta GetNextOutputTimestamp() const;
 
   // This is !is_null() iff Initialize() hasn't been called.
-  base::Callback<MessageLoop*()> message_loop_factory_cb_;
-  MessageLoop* message_loop_;
+  MessageLoopFactoryCB message_loop_factory_cb_;
+
+  scoped_refptr<base::MessageLoopProxy> message_loop_;
 
   scoped_refptr<DemuxerStream> demuxer_stream_;
   StatisticsCB statistics_cb_;