Use nullptr instead of 0 in WebAudio

Source/platform/audio/AudioDestination.cpp

 /*
  * 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 148 matching lines @@
     }
 
     for (unsigned i = 0; i < m_numberOfOutputChannels; ++i)
         m_renderBus->setChannelMemory(i, audioData[i], numberOfFrames);
 
     m_fifo->consume(m_renderBus.get(), numberOfFrames);
 }
 
 void AudioDestination::provideInput(AudioBus* bus, size_t framesToProcess)
 {
-    AudioBus* sourceBus = 0;
+    AudioBus* sourceBus = nullptr;
     if (m_inputFifo->framesInFifo() >= framesToProcess) {
         m_inputFifo->consume(m_inputBus.get(), framesToProcess);
         sourceBus = m_inputBus.get();
     }
 
     m_callback.render(sourceBus, bus, framesToProcess);
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)