Fix threading races on AudioDSPKernelProcessor::m_kernels

Source/core/platform/audio/AudioDSPKernelProcessor.h

Index: Source/core/platform/audio/AudioDSPKernelProcessor.h
diff --git a/Source/core/platform/audio/AudioDSPKernelProcessor.h b/Source/core/platform/audio/AudioDSPKernelProcessor.h
index 5c03835038f9b711d2781a70e71ef5949707e342..41c168a14e85008909cc7879e6bed01e6b562ba0 100644
--- a/Source/core/platform/audio/AudioDSPKernelProcessor.h
+++ b/Source/core/platform/audio/AudioDSPKernelProcessor.h
@@ -35,6 +35,7 @@
 #include "core/platform/audio/AudioProcessor.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
+#include "wtf/ThreadingPrimitives.h"
 #include "wtf/Vector.h"
 
 namespace WebCore {
@@ -69,6 +70,7 @@ public:
 
 protected:
     Vector<OwnPtr<AudioDSPKernel> > m_kernels;
+    mutable Mutex m_processLock;
     bool m_hasJustReset;
 };