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

content/renderer/pepper/video_decoder_shim.cc

Index: content/renderer/pepper/video_decoder_shim.cc
diff --git a/content/renderer/pepper/video_decoder_shim.cc b/content/renderer/pepper/video_decoder_shim.cc
index 8efb3d80c9831b61c0b2918449e5252315a33847..337afa3c70739616170c8cfb188986263ecec6bc 100644
--- a/content/renderer/pepper/video_decoder_shim.cc
+++ b/content/renderer/pepper/video_decoder_shim.cc
@@ -697,7 +697,7 @@ void VideoDecoderShim::DecoderImpl::Initialize(
 #if !defined(MEDIA_DISABLE_FFMPEG) && !defined(DISABLE_FFMPEG_VIDEO_DECODERS)
   {
     scoped_ptr<media::FFmpegVideoDecoder> ffmpeg_video_decoder(
-        new media::FFmpegVideoDecoder(base::ThreadTaskRunnerHandle::Get()));
+        new media::FFmpegVideoDecoder());
     ffmpeg_video_decoder->set_decode_nalus(true);
     decoder_ = ffmpeg_video_decoder.Pass();
   }