Use enum instead of string in MessageLoopFactory::GetMessageLoop*

media/tools/seek_tester/seek_tester.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This standalone binary is a helper for diagnosing seek behavior of the
 // demuxer setup in media/ code.  It answers the question: "if I ask the demuxer
 // to Seek to X ms, where will it actually seek to? (necessitating
 // frame-dropping until the original seek target is reached)".  Sample run:
 //
 // $ ./out/Debug/seek_tester .../LayoutTests/media/content/test.ogv 6300
@@ skipping 49 matching lines @@
   uint64 seek_target_ms;
   CHECK(base::StringToUint64(argv[2], &seek_target_ms));
   scoped_refptr<media::FileDataSource> file_data_source(
       new media::FileDataSource());
   CHECK(file_data_source->Initialize(argv[1]));
 
   DemuxerHostImpl host;
   MessageLoop loop;
   media::PipelineStatusCB quitter = base::Bind(&QuitMessageLoop, &loop);
   scoped_refptr<media::FFmpegDemuxer> demuxer(
-      new media::FFmpegDemuxer(&loop, file_data_source));
+      new media::FFmpegDemuxer(loop.message_loop_proxy(), file_data_source));
   demuxer->Initialize(&host, quitter);
   loop.Run();
 
   demuxer->Seek(base::TimeDelta::FromMilliseconds(seek_target_ms), quitter);
   loop.Run();
 
   uint64 audio_seeked_to_ms;
   uint64 video_seeked_to_ms;
   scoped_refptr<media::DemuxerStream> audio_stream(
       demuxer->GetStream(media::DemuxerStream::AUDIO));
@@ skipping 11 matching lines @@
         base::Bind(&TimestampExtractor, &video_seeked_to_ms, &loop));
     loop.Run();
     LOG(INFO) << "  video seeked to: " << video_seeked_to_ms << "ms";
   }
 
   demuxer->Stop(base::Bind(&MessageLoop::Quit, base::Unretained(&loop)));
   loop.Run();
 
   return 0;
 }