Remove unnecessary attribute "gain" in AudioBuffer and AudioBufferSourceNode interfaces

Source/modules/webaudio/AudioBuffer.h

Index: Source/modules/webaudio/AudioBuffer.h
diff --git a/Source/modules/webaudio/AudioBuffer.h b/Source/modules/webaudio/AudioBuffer.h
index 0609073a1a3a5af6c490009785bfec91a6ab3370..a7627bed7c57625d07a046809c4665ad74a56381 100644
--- a/Source/modules/webaudio/AudioBuffer.h
+++ b/Source/modules/webaudio/AudioBuffer.h
@@ -59,10 +59,6 @@ public:
     Float32Array* getChannelData(unsigned channelIndex);
     void zero();
 
-    // Scalar gain
-    double gain() const { return m_gain; }
-    void setGain(double gain) { m_gain = gain; }
-
     static float minAllowedSampleRate();
     static float maxAllowedSampleRate();
 protected:
@@ -70,7 +66,6 @@ protected:
     explicit AudioBuffer(AudioBus*);
     bool createdSuccessfully(unsigned desiredNumberOfChannels) const;
 
-    double m_gain; // scalar gain
     float m_sampleRate;
     size_t m_length;