Require use of AudioBus::create() to avoid ref-counting issues

Source/core/platform/audio/AudioBus.h

Index: Source/core/platform/audio/AudioBus.h
diff --git a/Source/core/platform/audio/AudioBus.h b/Source/core/platform/audio/AudioBus.h
index 9447f35c436f9998ea5a2f3d5cc11294adba4e10..6f4ed2b21877fb907d22264a84a69305939979af 100644
--- a/Source/core/platform/audio/AudioBus.h
+++ b/Source/core/platform/audio/AudioBus.h
@@ -66,7 +66,7 @@ public:
     // allocate indicates whether or not to initially have the AudioChannels created with managed storage.
     // Normal usage is to pass true here, in which case the AudioChannels will memory-manage their own storage.
     // If allocate is false then setChannelMemory() has to be called later on for each channel before the AudioBus is useable...
-    AudioBus(unsigned numberOfChannels, size_t length, bool allocate = true);
+    static PassRefPtr<AudioBus> create(unsigned numberOfChannels, size_t length, bool allocate = true);
 
     // Tells the given channel to use an externally allocated buffer.
     void setChannelMemory(unsigned channelIndex, float* storage, size_t length);
@@ -149,6 +149,8 @@ public:
 protected:
     AudioBus() { };
 
+    AudioBus(unsigned numberOfChannels, size_t length, bool allocate);
+
     void speakersCopyFrom(const AudioBus&);
     void discreteCopyFrom(const AudioBus&);
     void speakersSumFrom(const AudioBus&);