Use nullptr instead of 0 in WebAudio

Source/platform/audio/AudioChannel.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
@@ skipping 35 matching lines @@
     AudioChannel(float* storage, size_t length)
         : m_length(length)
         , m_rawPointer(storage)
         , m_silent(false)
     {
     }
 
     // Manage storage for us.
     explicit AudioChannel(size_t length)
         : m_length(length)
-        , m_rawPointer(0)
+        , m_rawPointer(nullptr)
         , m_silent(true)
     {
         m_memBuffer = adoptPtr(new AudioFloatArray(length));
     }
 
     // A "blank" audio channel -- must call set() before it's useful...
     AudioChannel()
         : m_length(0)
-        , m_rawPointer(0)
+        , m_rawPointer(nullptr)
         , m_silent(true)
     {
     }
 
     // Redefine the memory for this channel.
     // storage represents external memory not managed by this object.
     void set(float* storage, size_t length)
     {
         m_memBuffer.clear(); // cleanup managed storage
         m_rawPointer = storage;
@@ skipping 55 matching lines @@
     size_t m_length;
 
     float* m_rawPointer;
     OwnPtr<AudioFloatArray> m_memBuffer;
     bool m_silent;
 };
 
 } // namespace blink
 
 #endif // AudioChannel_h