Change GraphicsContext::createCompatibleBuffer to return something non-null

Source/platform/graphics/GraphicsContext.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008-2009 Torch Mobile, Inc.
  * Copyright (C) 2013 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.
@@ skipping 380 matching lines @@
     // ---------- End transformation methods -----------------
 
     // URL drawing
     void setURLForRect(const KURL&, const IntRect&);
     void setURLFragmentForRect(const String& name, const IntRect&);
     void addURLTargetAtPoint(const String& name, const IntPoint&);
     bool supportsURLFragments() { return printing(); }
 
     // Create an image buffer compatible with this context, with suitable resolution
     // for drawing into the buffer and then into this context.
-    PassOwnPtr<ImageBuffer> createCompatibleBuffer(const IntSize&, OpacityMode = NonOpaque) const;
+    PassOwnPtr<ImageBuffer> createRasterBuffer(const IntSize&, OpacityMode = NonOpaque) const;
 
     static void adjustLineToPixelBoundaries(FloatPoint& p1, FloatPoint& p2, float strokeWidth, StrokeStyle);
 
     void beginAnnotation(const AnnotationList&);
     void endAnnotation();
 
 private:
     const GraphicsContextState* immutableState() const { return m_paintState; }
 
     GraphicsContextState* mutableState()
@@ skipping 111 matching lines @@
     bool m_updatingControlTints : 1;
     bool m_accelerated : 1;
     bool m_isCertainlyOpaque : 1;
     bool m_printing : 1;
     bool m_antialiasHairlineImages : 1;
 };
 
 } // namespace WebCore
 
 #endif // GraphicsContext_h