Fix threading races on AudioDSPKernelProcessor::m_kernels

Source/core/platform/audio/AudioDSPKernelProcessor.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 17 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef AudioDSPKernelProcessor_h
 #define AudioDSPKernelProcessor_h
 
 #include "core/platform/audio/AudioBus.h"
 #include "core/platform/audio/AudioProcessor.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
+#include "wtf/ThreadingPrimitives.h"
 #include "wtf/Vector.h"
 
 namespace WebCore {
 
 class AudioBus;
 class AudioDSPKernel;
 class AudioProcessor;
 
 // AudioDSPKernelProcessor processes one input -> one output (N channels each)
 // It uses one AudioDSPKernel object per channel to do the processing, thus there is no cross-channel processing.
@@ skipping 14 matching lines @@
     virtual void process(const AudioBus* source, AudioBus* destination, size_t framesToProcess);
     virtual void reset();
     virtual void setNumberOfChannels(unsigned numberOfChannels);
     virtual unsigned numberOfChannels() const { return m_numberOfChannels; }
 
     virtual double tailTime() const OVERRIDE;
     virtual double latencyTime() const OVERRIDE;
 
 protected:
     Vector<OwnPtr<AudioDSPKernel> > m_kernels;
+    mutable Mutex m_processLock;
     bool m_hasJustReset;
 };
 
 } // namespace WebCore
 
 #endif // AudioDSPKernelProcessor_h