canvas: make a temporary buffer when a context doesn't exist.

Source/core/html/HTMLCanvasElement.h

 /*
  * Copyright (C) 2004, 2006, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 83 matching lines @@
         if (newSize == size())
             return;
         m_ignoreReset = true;
         setWidth(newSize.width());
         setHeight(newSize.height());
         m_ignoreReset = false;
         reset();
     }
 
     CanvasRenderingContext* getContext(const String&, CanvasContextAttributes* attributes = 0);
+    bool isPaintable() const;
 
     static String toEncodingMimeType(const String& mimeType);
     String toDataURL(const String& mimeType, const double* quality, ExceptionState&) const;
     String toDataURL(const String& mimeType, ExceptionState& exceptionState) const { return toDataURL(mimeType, 0, exceptionState); }
 
     // Used for rendering
     void didDraw(const FloatRect&);
     void notifyObserversCanvasChanged(const FloatRect&);
 
     void paint(GraphicsContext*, const LayoutRect&);
 
     GraphicsContext* drawingContext() const;
     GraphicsContext* existingDrawingContext() const;
 
     CanvasRenderingContext* renderingContext() const { return m_context.get(); }
 
     void ensureUnacceleratedImageBuffer();
     ImageBuffer* buffer() const;
-    Image* copiedImage(SourceDrawingBuffer) const;
+    PassRefPtr<Image> copiedImage(SourceDrawingBuffer) const;
     void clearCopiedImage();
 
     SecurityOrigin* securityOrigin() const;
     bool originClean() const { return m_originClean; }
     void setOriginTainted() { m_originClean = false; }
 
     AffineTransform baseTransform() const;
 
     bool is3D() const;
 
@@ skipping 75 matching lines @@
     bool m_imageBufferIsClear;
     OwnPtr<ImageBuffer> m_imageBuffer;
     mutable OwnPtr<GraphicsContextStateSaver> m_contextStateSaver;
 
     mutable RefPtr<Image> m_copiedImage; // FIXME: This is temporary for platforms that have to copy the image buffer to render (and for CSSCanvasValue).
 };
 
 } // namespace blink
 
 #endif // HTMLCanvasElement_h