Use nullptr instead of 0 in WebAudio

Source/platform/audio/AudioDSPKernel.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 28 matching lines @@
 
 class PLATFORM_EXPORT AudioDSPKernel {
 public:
     AudioDSPKernel(AudioDSPKernelProcessor* kernelProcessor)
         : m_kernelProcessor(kernelProcessor)
         , m_sampleRate(kernelProcessor->sampleRate())
     {
     }
 
     AudioDSPKernel(float sampleRate)
-        : m_kernelProcessor(0)
+        : m_kernelProcessor(nullptr)
         , m_sampleRate(sampleRate)
     {
     }
 
     virtual ~AudioDSPKernel();
 
     // Subclasses must override process() to do the processing and reset() to reset DSP state.
     virtual void process(const float* source, float* destination, size_t framesToProcess) = 0;
     virtual void reset() = 0;
 
@@ skipping 14 matching lines @@
     // do that because AudioDSPKernel can be allocated in audio threads
     // (which are not registered to Oilpan).
     GC_PLUGIN_IGNORE("http://crbug.com/404578")
     AudioDSPKernelProcessor* m_kernelProcessor;
     float m_sampleRate;
 };
 
 } // namespace blink
 
 #endif // AudioDSPKernel_h