MediaStream audio object graph untangling and clean-ups.

content/renderer/media/media_stream_audio_source.cc

Index: content/renderer/media/media_stream_audio_source.cc
diff --git a/content/renderer/media/media_stream_audio_source.cc b/content/renderer/media/media_stream_audio_source.cc
index c643140e4dbdb6ef5d3d294477a3b7f3cb4cd785..bf9c4868436a128471d6e30778c182fa0412dc28 100644
--- a/content/renderer/media/media_stream_audio_source.cc
+++ b/content/renderer/media/media_stream_audio_source.cc
@@ -5,6 +5,7 @@
 #include "content/renderer/media/media_stream_audio_source.h"
 
 #include "content/renderer/render_frame_impl.h"
+#include "third_party/WebKit/public/platform/WebMediaStreamSource.h"
 
 namespace content {
 
@@ -24,6 +25,16 @@ MediaStreamAudioSource::MediaStreamAudioSource()
 
 MediaStreamAudioSource::~MediaStreamAudioSource() {}
 
+// static
+MediaStreamAudioSource* MediaStreamAudioSource::From(
+    const blink::WebMediaStreamSource& source) {
+  if (source.isNull() ||
+      source.type() != blink::WebMediaStreamSource::TypeAudio) {
+    return nullptr;
+  }
+  return static_cast<MediaStreamAudioSource*>(source.extraData());
+}
+
 void MediaStreamAudioSource::DoStopSource() {
   if (audio_capturer_.get())
     audio_capturer_->Stop();