Support multichannel audio stream more than 2 in MediaStreamDestinationNode

third_party/WebKit/Source/modules/webaudio/MediaStreamAudioDestinationNode.h

Index: third_party/WebKit/Source/modules/webaudio/MediaStreamAudioDestinationNode.h
diff --git a/third_party/WebKit/Source/modules/webaudio/MediaStreamAudioDestinationNode.h b/third_party/WebKit/Source/modules/webaudio/MediaStreamAudioDestinationNode.h
index f8bd9fe773706db49db2226bf0ffcc8bf2f56696..292c09a70b1f6d7075176046363e4ea55fb7891d 100644
--- a/third_party/WebKit/Source/modules/webaudio/MediaStreamAudioDestinationNode.h
+++ b/third_party/WebKit/Source/modules/webaudio/MediaStreamAudioDestinationNode.h
@@ -46,6 +46,9 @@ public:
 
     // AudioHandler.
     void process(size_t framesToProcess) override;
+    void setChannelCount(unsigned long, ExceptionState&) override;
+
+    unsigned long maxChannelCount() const;
 
 private:
     MediaStreamAudioDestinationHandler(AudioNode&, size_t numberOfChannels);
@@ -55,6 +58,9 @@ private:
     // This Persistent doesn't make a reference cycle.
     Persistent<MediaStream> m_stream;
     Persistent<MediaStreamSource> m_source;
+
+    // This internal mix bus is for up/down mixing the input to the actual
+    // number of channels in the destination.
     RefPtr<AudioBus> m_mixBus;
 };