Add constructors for WebAudio nodes

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

Index: third_party/WebKit/Source/modules/webaudio/GainNode.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/GainNode.cpp b/third_party/WebKit/Source/modules/webaudio/GainNode.cpp
index 190e61a54f713778a7dcb6c924c56d9dbe1af6c0..7f026769d2c3825cc433ab2c9408261899d2a5ff 100644
--- a/third_party/WebKit/Source/modules/webaudio/GainNode.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/GainNode.cpp
@@ -25,6 +25,7 @@
 #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 {
@@ -138,6 +139,21 @@ GainNode* GainNode::create(BaseAudioContext& context, ExceptionState& exceptionS
     return new GainNode(context);
 }
 
+GainNode* GainNode::create(BaseAudioContext* context, const GainOptions& options, ExceptionState& exceptionState)
+{
+    GainNode* node = create(*context, exceptionState);
+
+    if (!node)
+        return nullptr;
+
+    node->handleChannelOptions(options, exceptionState);
+
+    if (options.hasGain())
+        node->gain()->setValue(options.gain());
+
+    return node;
+}
+
 AudioParam* GainNode::gain() const
 {
     return m_gain;