Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/audio/HRTFKernel.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 95 matching lines @@
     fftFrame.doInverseFFT(channel->mutableData());
 
     return channel.release();
 }
 
 // Interpolates two kernels with x: 0 -> 1 and returns the result.
 PassRefPtr<HRTFKernel> HRTFKernel::createInterpolatedKernel(HRTFKernel* kernel1, HRTFKernel* kernel2, float x)
 {
     ASSERT(kernel1 && kernel2);
     if (!kernel1 || !kernel2)
-        return 0;
+        return nullptr;
 
     ASSERT(x >= 0.0 && x < 1.0);
     x = min(1.0f, max(0.0f, x));
 
     float sampleRate1 = kernel1->sampleRate();
     float sampleRate2 = kernel2->sampleRate();
     ASSERT(sampleRate1 == sampleRate2);
     if (sampleRate1 != sampleRate2)
-        return 0;
+        return nullptr;
 
     float frameDelay = (1 - x) * kernel1->frameDelay() + x * kernel2->frameDelay();
 
     OwnPtr<FFTFrame> interpolatedFrame = FFTFrame::createInterpolatedFrame(*kernel1->fftFrame(), *kernel2->fftFrame(), x);
     return HRTFKernel::create(interpolatedFrame.release(), frameDelay, sampleRate1);
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)