Refactor ResourceLoadPriorityOptimizer to avoid walking render tree

Source/core/rendering/RenderObject.h

Index: Source/core/rendering/RenderObject.h
diff --git a/Source/core/rendering/RenderObject.h b/Source/core/rendering/RenderObject.h
index 066ee73d80ecbaf37aa2742d1ed070f846b210ef..a74529cc650f86d2a6bd8db31adbffc47658fab7 100644
--- a/Source/core/rendering/RenderObject.h
+++ b/Source/core/rendering/RenderObject.h
@@ -668,8 +668,7 @@ public:
     // 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(); }