MediaStream audio: Refactor 3 separate "glue" implementations into one.

content/renderer/media/media_stream_center.cc

Index: content/renderer/media/media_stream_center.cc
diff --git a/content/renderer/media/media_stream_center.cc b/content/renderer/media/media_stream_center.cc
index 2f84bd8eb2be103006c91c73cc75aaf3952521a6..afaae406f9a4784623bdf726d66b42a1e3534d87 100644
--- a/content/renderer/media/media_stream_center.cc
+++ b/content/renderer/media/media_stream_center.cc
@@ -19,6 +19,7 @@
 #include "content/renderer/media/media_stream_source.h"
 #include "content/renderer/media/media_stream_video_source.h"
 #include "content/renderer/media/media_stream_video_track.h"
+#include "content/renderer/media/webaudio_media_stream_source.h"
 #include "content/renderer/media/webrtc/peer_connection_dependency_factory.h"
 #include "content/renderer/media/webrtc_local_audio_source_provider.h"
 #include "third_party/WebKit/public/platform/WebMediaConstraints.h"
@@ -41,14 +42,27 @@ namespace {
 void CreateNativeAudioMediaStreamTrack(
     const blink::WebMediaStreamTrack& track,
     PeerConnectionDependencyFactory* factory) {

[perkj_chrome, 2016/04/08 14:05:42]

please remove |factory| I think this might be the last dependency in this class.

[miu, 2016/04/19 00:40:22]

Done.  Yes it is!  :)

I've removed |rtc_factory_| from MediaStreamCenter, but I added a TODO to remove
the unnecessary ctor args in a follow-up change since I didn't want this change
to spread-out into even more files.  ;)

-  DCHECK(!MediaStreamAudioTrack::From(track));
   blink::WebMediaStreamSource source = track.source();
-  DCHECK_EQ(source.getType(), blink::WebMediaStreamSource::TypeAudio);
-  if (source.remote()) {
-    factory->CreateRemoteAudioTrack(track);
-  } else {
-    factory->CreateLocalAudioTrack(track);
+  MediaStreamAudioSource* media_stream_source =
+      MediaStreamAudioSource::From(source);
+
+  // At this point, a MediaStreamAudioSource instance must exist.  The one
+  // exception is when a WebAudio destination node is acting as a source of
+  // audio.
+  //
+  // TODO(miu): This needs to be moved to an appropriate location.  A WebAudio
+  // source should have been created before this method was called so that this
+  // special case code isn't needed here.
+  if (!media_stream_source && source.requiresAudioConsumer()) {
+    DVLOG(1) << "Creating WebAudio media stream source.";
+    media_stream_source = new WebAudioMediaStreamSource(&source);
+    source.setExtraData(media_stream_source);  // Takes ownership.
   }
+
+  if (media_stream_source)
+    media_stream_source->ConnectToTrack(track);
+  else
+    LOG(DFATAL) << "WebMediaStreamSource missing its MediaStreamAudioSource.";
 }
 
 void CreateNativeVideoMediaStreamTrack(