Initialize value since calculateFinalValues may fail to do so.

Source/modules/webaudio/BiquadDSPKernel.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:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 44 matching lines @@
 
     virtual double tailTime() const OVERRIDE;
     virtual double latencyTime() const OVERRIDE;
 
 protected:
     Biquad m_biquad;
     BiquadProcessor* biquadProcessor() { return static_cast<BiquadProcessor*>(processor()); }
 
     // To prevent audio glitches when parameters are changed,
     // dezippering is used to slowly change the parameters.
-    // |useSmoothing| implies that we want to update using the
-    // smoothed values. Otherwise the final target values are
-    // used. If |forceUpdate| is true, we update the coefficients even
-    // if they are not dirty. (Used when computing the frequency
-    // response.)
-    void updateCoefficientsIfNecessary(bool useSmoothing, bool forceUpdate);
+    void updateCoefficientsIfNecessary();
+    // Update the biquad cofficients with the given parameters
+    void updateCoefficients(double frequency, double Q, double gain, double detune);
+
+private:
+    // Synchronize process() with getting and setting the filter coefficients.
+    mutable Mutex m_processLock;
 };
 
 } // namespace WebCore
 
 #endif // BiquadDSPKernel_h