Remove unnecessary attribute "gain" in AudioBuffer and AudioBufferSourceNode interfaces

Source/modules/webaudio/AudioBufferSourceNode.cpp

Index: Source/modules/webaudio/AudioBufferSourceNode.cpp
diff --git a/Source/modules/webaudio/AudioBufferSourceNode.cpp b/Source/modules/webaudio/AudioBufferSourceNode.cpp
index e7257bfc62a98a5608bec9cc0f436c5f783f4ee5..90408b8abab3310cb1a0ee19aa60d756f5c09ff0 100644
--- a/Source/modules/webaudio/AudioBufferSourceNode.cpp
+++ b/Source/modules/webaudio/AudioBufferSourceNode.cpp
@@ -65,13 +65,11 @@ AudioBufferSourceNode::AudioBufferSourceNode(AudioContext* context, float sample
     , m_isGrain(false)
     , m_grainOffset(0.0)
     , m_grainDuration(DefaultGrainDuration)
-    , m_lastGain(1.0)
     , m_pannerNode(0)
 {
     ScriptWrappable::init(this);
     setNodeType(NodeTypeAudioBufferSource);
 
-    m_gain = AudioParam::create(context, "gain", 1.0, 0.0, 1.0);
     m_playbackRate = AudioParam::create(context, "playbackRate", 1.0, 0.0, MaxRate);
 
     // Default to mono.  A call to setBuffer() will set the number of output channels to that of the buffer.
@@ -133,9 +131,6 @@ void AudioBufferSourceNode::process(size_t framesToProcess)
             return;
         }
 
-        // Apply the gain (in-place) to the output bus.
-        float totalGain = gain()->value() * m_buffer->gain();
-        outputBus->copyWithGainFrom(*outputBus, &m_lastGain, totalGain);

[Raymond Toy, 2014/04/07 20:17:12]

Do we still need to do some kind of copy here or does outputBus already contain
the desired data?

[KhNo, 2014/04/08 02:27:16]

It is just for applying gain to outputBus itself.
First parameter is outputBus.
Inside of copyWithGainFrom() it is filtered out if targetGain and lastMixGain
are same.
We don't need to do this.

         outputBus->clearSilentFlag();
     } else {
         // Too bad - the tryLock() failed.  We must be in the middle of changing buffers and were already outputting silence anyway.