media::FFmpegVideoDecoder: remove ctor param |task_runner| and use a ThreadChecker instead.

media/renderers/default_renderer_factory.cc

 // Copyright 2014 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.
 
 #include "media/renderers/default_renderer_factory.h"
 
 #include "base/bind.h"
 #include "build/build_config.h"
 #include "base/single_thread_task_runner.h"
 #include "media/base/media_log.h"
@@ skipping 64 matching lines @@
          (gpu_factories_->GetTaskRunner() == media_task_runner.get()));
 
   if (gpu_factories_)
     video_decoders.push_back(new GpuVideoDecoder(gpu_factories_));
 
 #if !defined(MEDIA_DISABLE_LIBVPX)
   video_decoders.push_back(new VpxVideoDecoder(media_task_runner));
 #endif
 
 #if !defined(MEDIA_DISABLE_FFMPEG) && !defined(DISABLE_FFMPEG_VIDEO_DECODERS)
-  video_decoders.push_back(new FFmpegVideoDecoder(media_task_runner));
+  video_decoders.push_back(new FFmpegVideoDecoder());
 #endif
 
   scoped_ptr<VideoRenderer> video_renderer(new VideoRendererImpl(
       media_task_runner, worker_task_runner, video_renderer_sink,
       video_decoders.Pass(), true, gpu_factories_, media_log_));
 
   // Create renderer.
   return scoped_ptr<Renderer>(new RendererImpl(
       media_task_runner, audio_renderer.Pass(), video_renderer.Pass()));
 }
 
 }  // namespace media