Add constructors for WebAudio nodes

third_party/WebKit/Source/modules/webaudio/GainNode.cpp

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 #include "modules/webaudio/GainNode.h"
 #include "modules/webaudio/AudioNodeInput.h"
 #include "modules/webaudio/AudioNodeOutput.h"
+#include "modules/webaudio/GainOptions.h"
 #include "platform/audio/AudioBus.h"
 
 namespace blink {
 
 GainHandler::GainHandler(AudioNode& node, float sampleRate, AudioParamHandler& gain)
     : AudioHandler(NodeTypeGain, node, sampleRate)
     , m_lastGain(1.0)
     , m_gain(gain)
     , m_sampleAccurateGainValues(ProcessingSizeInFrames) // FIXME: can probably share temp buffer in context
 {
@@ skipping 93 matching lines @@
     DCHECK(isMainThread());
 
     if (context.isContextClosed()) {
         context.throwExceptionForClosedState(exceptionState);
         return nullptr;
     }
 
     return new GainNode(context);
 }
 
+GainNode* GainNode::create(BaseAudioContext* context, const GainOptions& options, ExceptionState& exceptionState)
+{
+    GainNode* node = create(*context, exceptionState);
+
+    if (!node)
+        return node;

[hongchan, 2016/09/12 18:56:32]

return nullptr;

+
+    node->handleChannelOptions(options, exceptionState);
+
+    if (options.hasGain())
+        node->gain()->setValue(options.gain());
+
+    return node;
+}
+
 AudioParam* GainNode::gain() const
 {
     return m_gain;
 }
 
 DEFINE_TRACE(GainNode)
 {
     visitor->trace(m_gain);
     AudioNode::trace(visitor);
 }
 
 } // namespace blink