Bug 984498: add new a parameter(audiochannel type) to AudioContext API. r=roc

dom/webidl/AudioContext.webidl

@@ -13,7 +13,8 @@
 callback DecodeSuccessCallback = void (AudioBuffer decodedData);
 callback DecodeErrorCallback = void ();
 
-[Constructor]
+[Constructor,
+ Constructor(AudioChannel audioChannelType)]
 interface AudioContext : EventTarget {
 
     readonly attribute AudioDestinationNode destination;
@@ -28,7 +29,7 @@ interface AudioContext : EventTarget {
                          DecodeSuccessCallback successCallback,
                          optional DecodeErrorCallback errorCallback);
 
-    // AudioNode creation 
+    // AudioNode creation
     [NewObject]
     AudioBufferSourceNode createBufferSource();