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

Source/core/platform/audio/AudioFIFO.h

Index: Source/core/platform/audio/AudioFIFO.h
diff --git a/Source/core/platform/audio/AudioFIFO.h b/Source/core/platform/audio/AudioFIFO.h
index a5c1dca4781e637952560af26332414cbe0b86d2..a744d10eb62a109b0a044ed9f4a61a3e3113af4b 100644
--- a/Source/core/platform/audio/AudioFIFO.h
+++ b/Source/core/platform/audio/AudioFIFO.h
@@ -55,7 +55,7 @@ private:
     void findWrapLengths(size_t index, size_t providerSize, size_t& part1Length, size_t& part2Length);
     
     // The FIFO itself. In reality, the FIFO is a circular buffer.
-    AudioBus m_fifoAudioBus;
+    RefPtr<AudioBus> m_fifoAudioBus;
 
     // The total available space in the FIFO.
     size_t m_fifoLength;