Oilpan: keep ImageData on the heap by default.

Source/core/html/HTMLCanvasElement.cpp

 /*
  * Copyright (C) 2004, 2006, 2007 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 466 matching lines @@
     return AtomicString(toDataURLInternal("image/png", 0, FrontBuffer));
 }
 
 String HTMLCanvasElement::toDataURLInternal(const String& mimeType, const double* quality, SourceDrawingBuffer sourceBuffer) const
 {
     if (!isPaintable())
         return String("data:,");
 
     String encodingMimeType = toEncodingMimeType(mimeType);
     if (!m_context) {
-        RefPtrWillBeRawPtr<ImageData> imageData = ImageData::create(m_size);
+        ImageData* imageData = ImageData::create(m_size);

[Justin Novosad, 2015/05/06 20:14:03]

In this case the image data is just a temporary local, and it can be wrapping a
pretty large buffer. Would it be worth forcibly destroying it instead of just
letting it go out of scope?

         return ImageDataBuffer(imageData->size(), imageData->data()->data()).toDataURL(encodingMimeType, quality);
     }
 
     if (m_context->is3d()) {
         // Get non-premultiplied data because of inaccurate premultiplied alpha conversion of buffer()->toDataURL().
-        RefPtrWillBeRawPtr<ImageData> imageData =
-            toWebGLRenderingContextBase(m_context.get())->paintRenderingResultsToImageData(sourceBuffer);
+        ImageData* imageData = toWebGLRenderingContextBase(m_context.get())->paintRenderingResultsToImageData(sourceBuffer);

[Justin Novosad, 2015/05/06 20:14:03]

same here

         if (imageData)
             return ImageDataBuffer(imageData->size(), imageData->data()->data()).toDataURL(encodingMimeType, quality);
         m_context->paintRenderingResultsToCanvas(sourceBuffer);
     }
 
     return buffer()->toDataURL(encodingMimeType, quality);
 }
 
 String HTMLCanvasElement::toDataURL(const String& mimeType, const ScriptValue& qualityArgument, ExceptionState& exceptionState) const
 {
@@ skipping 372 matching lines @@
 {
     return FloatSize(width(), height());
 }
 
 bool HTMLCanvasElement::isOpaque() const
 {
     return m_context && !m_context->hasAlpha();
 }
 
 } // blink