Implement StereoPannerNode for robust stereo panning

Source/modules/webaudio/AudioContext.h

Index: Source/modules/webaudio/AudioContext.h
diff --git a/Source/modules/webaudio/AudioContext.h b/Source/modules/webaudio/AudioContext.h
index 1e54668a91992c2f8d2b5ac42efa20c049dd3414..4971b38d60a0f3d35b06283ffb29a93d0ef17a06 100644
--- a/Source/modules/webaudio/AudioContext.h
+++ b/Source/modules/webaudio/AudioContext.h
@@ -68,6 +68,7 @@ class OscillatorNode;
 class PannerNode;
 class PeriodicWave;
 class ScriptProcessorNode;
+class StereoPannerNode;
 class WaveShaperNode;
 
 // AudioContext is the cornerstone of the web audio API and all AudioNodes are created from it.
@@ -122,6 +123,7 @@ public:
     ScriptProcessorNode* createScriptProcessor(size_t bufferSize, ExceptionState&);
     ScriptProcessorNode* createScriptProcessor(size_t bufferSize, size_t numberOfInputChannels, ExceptionState&);
     ScriptProcessorNode* createScriptProcessor(size_t bufferSize, size_t numberOfInputChannels, size_t numberOfOutputChannels, ExceptionState&);
+    StereoPannerNode* createStereoPanner();
     ChannelSplitterNode* createChannelSplitter(ExceptionState&);
     ChannelSplitterNode* createChannelSplitter(size_t numberOfOutputs, ExceptionState&);
     ChannelMergerNode* createChannelMerger(ExceptionState&);