Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/graphics/ImageBuffer.cpp

 /*
  * Copyright (c) 2008, Google Inc. All rights reserved.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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
@@ skipping 238 matching lines @@
                 lookUpTable[SkColorGetB(color)]);
         }
     }
 }
 
 PassRefPtr<SkColorFilter> ImageBuffer::createColorSpaceFilter(ColorSpace srcColorSpace,
     ColorSpace dstColorSpace)
 {
     const uint8_t* lut = ColorSpaceUtilities::getConversionLUT(dstColorSpace, srcColorSpace);
     if (!lut)
-        return 0;
+        return nullptr;
 
     return adoptRef(SkTableColorFilter::CreateARGB(0, lut, lut, lut));
 }
 
 template <Multiply multiplied>
 PassRefPtr<Uint8ClampedArray> getImageData(const IntRect& rect, GraphicsContext* context, const IntSize& size)
 {
     float area = 4.0f * rect.width() * rect.height();
     if (area > static_cast<float>(std::numeric_limits<int>::max()))
-        return 0;
+        return nullptr;
 
     RefPtr<Uint8ClampedArray> result = Uint8ClampedArray::createUninitialized(rect.width() * rect.height() * 4);
 
     unsigned char* data = result->data();
 
     if (rect.x() < 0
         || rect.y() < 0
         || rect.maxX() > size.width()
         || rect.maxY() > size.height())
         result->zeroFill();
@@ skipping 119 matching lines @@
     if (!encodeImage(imageData, mimeType, quality, &encodedImage))
         return "data:,";
 
     Vector<char> base64Data;
     base64Encode(encodedImage, base64Data);
 
     return "data:" + mimeType + ";base64," + base64Data;
 }
 
 } // namespace WebCore