Enable Oilpan by default for webaudio/

Source/modules/webaudio/ChannelMergerNode.cpp

Index: Source/modules/webaudio/ChannelMergerNode.cpp
diff --git a/Source/modules/webaudio/ChannelMergerNode.cpp b/Source/modules/webaudio/ChannelMergerNode.cpp
index eaba95fc65d192fcdae4b683dc7b9688f5d307fa..3a7bea270de5c7f67d4d0579eca8e53391a30219 100644
--- a/Source/modules/webaudio/ChannelMergerNode.cpp
+++ b/Source/modules/webaudio/ChannelMergerNode.cpp
@@ -40,12 +40,12 @@ const unsigned DefaultNumberOfOutputChannels = 1;
 
 namespace blink {
 
-PassRefPtrWillBeRawPtr<ChannelMergerNode> ChannelMergerNode::create(AudioContext* context, float sampleRate, unsigned numberOfInputs)
+ChannelMergerNode* ChannelMergerNode::create(AudioContext* context, float sampleRate, unsigned numberOfInputs)
 {
     if (!numberOfInputs || numberOfInputs > AudioContext::maxNumberOfChannels())
-        return nullptr;
+        return 0;
 
-    return adoptRefWillBeNoop(new ChannelMergerNode(context, sampleRate, numberOfInputs));
+    return adoptRefCountedGarbageCollected(new ChannelMergerNode(context, sampleRate, numberOfInputs));
 }
 
 ChannelMergerNode::ChannelMergerNode(AudioContext* context, float sampleRate, unsigned numberOfInputs)