Backed out changeset eab0db5216b7 (bug 1395593) for regression on macOS and Windows as requested by jesup. r=backout a=backout

MozReview-Commit-ID: E7owt3xoe7c

dom/media/GraphDriver.h

@@ -445,12 +445,6 @@ public:
     return this;
   }
 
-  uint32_t OutputChannelCount()
-  {
-    MOZ_ASSERT(mOuputChannels != 0 && mOuputChannels <= 8);
-    return mOuputChannels;
-  }
-
   /* Enqueue a promise that is going to be resolved when a specific operation
    * occurs on the cubeb stream. */
   void EnqueueStreamAndPromiseForOperation(MediaStream* aStream,

dom/media/MediaStreamGraph.cpp

@@ -948,8 +948,7 @@ MediaStreamGraphImpl::PlayAudio(MediaStream* aStream)
 
     // Need unique id for stream & track - and we want it to match the inserter
     output.WriteTo(LATENCY_STREAM_ID(aStream, track->GetID()),
-                                     mMixer,
-                                     CurrentDriver()->AsAudioCallbackDriver()->OutputChannelCount(),
+                                     mMixer, AudioChannelCount(),
                                      mSampleRate);
   }
   return ticksWritten;