Use nullptr instead of 0 in WebAudio

Source/modules/webaudio/MediaElementAudioSourceNode.cpp

 /*
  * Copyright (C) 2011, 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 46 matching lines @@
     initialize();
 }
 
 MediaElementAudioSourceNode::~MediaElementAudioSourceNode()
 {
     ASSERT(!isInitialized());
 }
 
 void MediaElementAudioSourceNode::dispose()
 {
-    m_mediaElement->setAudioSourceNode(0);
+    m_mediaElement->setAudioSourceNode(nullptr);
     uninitialize();
     AudioSourceNode::dispose();
 }
 
 void MediaElementAudioSourceNode::setFormat(size_t numberOfChannels, float sourceSampleRate)
 {
     if (numberOfChannels != m_sourceNumberOfChannels || sourceSampleRate != m_sourceSampleRate) {
         if (!numberOfChannels || numberOfChannels > AudioContext::maxNumberOfChannels() || !AudioUtilities::isValidAudioBufferSampleRate(sourceSampleRate)) {
             // process() will generate silence for these uninitialized values.
             WTF_LOG(Media, "MediaElementAudioSourceNode::setFormat(%u, %f) - unhandled format change", static_cast<unsigned>(numberOfChannels), sourceSampleRate);
@@ skipping 80 matching lines @@
 DEFINE_TRACE(MediaElementAudioSourceNode)
 {
     visitor->trace(m_mediaElement);
     AudioSourceNode::trace(visitor);
     AudioSourceProviderClient::trace(visitor);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)