Change GraphicsContext::createCompatibleBuffer to return something non-null

Source/platform/graphics/CrossfadeGeneratedImage.cpp

 /*
  * Copyright (C) 2011 Apple 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 81 matching lines @@
     context->translate(dstRect.x(), dstRect.y());
     if (dstRect.size() != srcRect.size())
         context->scale(dstRect.width() / srcRect.width(), dstRect.height() / srcRect.height());
     context->translate(-srcRect.x(), -srcRect.y());
 
     drawCrossfade(context);
 }
 
 void CrossfadeGeneratedImage::drawPattern(GraphicsContext* context, const FloatRect& srcRect, const FloatSize& scale, const FloatPoint& phase, CompositeOperator compositeOp, const FloatRect& dstRect, blink::WebBlendMode blendMode, const IntSize& repeatSpacing)
 {
-    OwnPtr<ImageBuffer> imageBuffer = context->createCompatibleBuffer(m_size);
+    OwnPtr<ImageBuffer> imageBuffer = context->createRasterBuffer(m_size);
     if (!imageBuffer)
         return;
 
     // Fill with the cross-faded image.
     GraphicsContext* graphicsContext = imageBuffer->context();
     drawCrossfade(graphicsContext);
 
     // Tile the image buffer into the context.
     imageBuffer->drawPattern(context, srcRect, scale, phase, compositeOp, dstRect, blendMode, repeatSpacing);
 }
 
 }