Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/graphics/gpu/DrawingBuffer.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:
  *
  *     * 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 768 matching lines @@
 }
 
 void DrawingBuffer::paintRenderingResultsToCanvas(ImageBuffer* imageBuffer)
 {
     paintFramebufferToCanvas(framebuffer(), size().width(), size().height(), !m_attributes.premultipliedAlpha, imageBuffer);
 }
 
 PassRefPtr<Uint8ClampedArray> DrawingBuffer::paintRenderingResultsToImageData(int& width, int& height)
 {
     if (m_attributes.premultipliedAlpha)
-        return 0;
+        return nullptr;
 
     width = size().width();
     height = size().height();
 
     Checked<int, RecordOverflow> dataSize = 4;
     dataSize *= width;
     dataSize *= height;
     if (dataSize.hasOverflowed())
-        return 0;
+        return nullptr;
 
     RefPtr<Uint8ClampedArray> pixels = Uint8ClampedArray::createUninitialized(width * height * 4);
 
     m_context->bindFramebuffer(GL_FRAMEBUFFER, framebuffer());
     readBackFramebuffer(pixels->data(), width, height, ReadbackRGBA, WebGLImageConversion::AlphaDoNothing);
     flipVertically(pixels->data(), width, height);
 
     return pixels.release();
 }
 
@@ skipping 85 matching lines @@
     }
 }
 
 void DrawingBuffer::texImage2DResourceSafe(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, GLint unpackAlignment)
 {
     ASSERT(unpackAlignment == 1 || unpackAlignment == 2 || unpackAlignment == 4 || unpackAlignment == 8);
     m_context->texImage2D(target, level, internalformat, width, height, border, format, type, 0);
 }
 
 } // namespace WebCore