Refactor ResourceLoadPriorityOptimizer to avoid walking render tree

Source/core/rendering/RenderObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 650 matching lines @@
 
     void updateFillImages(const FillLayer*, const FillLayer*);
     void updateImage(StyleImage*, StyleImage*);
     void updateShapeImage(const ShapeValue*, const ShapeValue*);
 
     virtual void paint(PaintInfo&, const LayoutPoint&);
 
     // Subclasses must reimplement this method to compute the size and position
     // of this object and all its descendants.
     virtual void layout() = 0;
-    virtual void didLayout(ResourceLoadPriorityOptimizer&);
-    virtual void didScroll(ResourceLoadPriorityOptimizer&);
+    virtual bool updateImageLoadingPriorities() { return false; }
 
     /* This function performs a layout only if one is needed. */
     void layoutIfNeeded() { if (needsLayout()) layout(); }
 
     void forceLayout();
     void forceChildLayout();
 
     // True if we can abort layout, leaving a partially laid out tree.
     virtual bool supportsPartialLayout() const { return false; }
 
@@ skipping 744 matching lines @@
 void showTree(const WebCore::RenderObject*);
 void showLineTree(const WebCore::RenderObject*);
 void showRenderTree(const WebCore::RenderObject* object1);
 // We don't make object2 an optional parameter so that showRenderTree
 // can be called from gdb easily.
 void showRenderTree(const WebCore::RenderObject* object1, const WebCore::RenderObject* object2);
 
 #endif
 
 #endif // RenderObject_h