Add channel_count parameter back to AudioBuffer creation methods.

media/filters/ffmpeg_audio_decoder.cc

Index: media/filters/ffmpeg_audio_decoder.cc
diff --git a/media/filters/ffmpeg_audio_decoder.cc b/media/filters/ffmpeg_audio_decoder.cc
index c8f8f50a1a7bf574664645c44b2f29782d36febd..3cb69c050d9643ad246be019af4dd8719daa35dc 100644
--- a/media/filters/ffmpeg_audio_decoder.cc
+++ b/media/filters/ffmpeg_audio_decoder.cc
@@ -92,6 +92,7 @@ static int GetAudioBuffer(struct AVCodecContext* s, AVFrame* frame, int flags) {
   scoped_refptr<AudioBuffer> buffer = AudioBuffer::CreateBuffer(
       sample_format,
       ChannelLayoutToChromeChannelLayout(s->channel_layout, s->channels),
+      channels,
       s->sample_rate,
       frames_required);