MediaStream audio object graph untangling and clean-ups.

content/renderer/media/speech_recognition_audio_sink.cc

Index: content/renderer/media/speech_recognition_audio_sink.cc
diff --git a/content/renderer/media/speech_recognition_audio_sink.cc b/content/renderer/media/speech_recognition_audio_sink.cc
index 1035aff13da4a11c1182c72e60c6067ee4fd6cc4..3beb5a8d6b226e8db989167bb020c25d03efc746 100644
--- a/content/renderer/media/speech_recognition_audio_sink.cc
+++ b/content/renderer/media/speech_recognition_audio_sink.cc
@@ -61,11 +61,8 @@ SpeechRecognitionAudioSink::~SpeechRecognitionAudioSink() {
 // static
 bool SpeechRecognitionAudioSink::IsSupportedTrack(
     const blink::WebMediaStreamTrack& track) {
-  if (track.source().type() != blink::WebMediaStreamSource::TypeAudio)
-    return false;
-
   MediaStreamAudioSource* native_source =
-      static_cast<MediaStreamAudioSource*>(track.source().extraData());
+      MediaStreamAudioSource::From(track.source());
   if (!native_source)
     return false;