Oilpan: keep ImageData on the heap by default.

Source/core/html/canvas/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 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 963 matching lines @@
     drawingBuffer()->commit();
     if (!canvas()->buffer()->copyRenderingResultsFromDrawingBuffer(drawingBuffer(), sourceBuffer)) {
         canvas()->ensureUnacceleratedImageBuffer();
         if (canvas()->hasImageBuffer())
             drawingBuffer()->paintRenderingResultsToCanvas(canvas()->buffer());
     }
 
     return true;
 }
 
-PassRefPtrWillBeRawPtr<ImageData> WebGLRenderingContextBase::paintRenderingResultsToImageData(SourceDrawingBuffer sourceBuffer)
+ImageData* WebGLRenderingContextBase::paintRenderingResultsToImageData(SourceDrawingBuffer sourceBuffer)
 {
     if (isContextLost())
         return nullptr;
     if (m_requestedAttributes.premultipliedAlpha())
         return nullptr;
 
     clearIfComposited();
     drawingBuffer()->commit();
     ScopedFramebufferRestorer restorer(this);
     int width, height;
@@ skipping 5098 matching lines @@
     return m_sharedWebGraphicsContext3D ? m_sharedWebGraphicsContext3D->drawingBuffer() : 0;
 }
 #else
 DrawingBuffer* WebGLRenderingContextBase::drawingBuffer() const
 {
     return m_drawingBuffer.get();
 }
 #endif
 
 } // namespace blink