Refactor ResourceLoadPriorityOptimizer to avoid walking render tree

Source/core/frame/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple 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 416 matching lines @@
     void deferredRepaintTimerFired(Timer<FrameView>*);
     void doDeferredRepaints();
     void updateDeferredRepaintDelayAfterRepaint();
     double adjustedDeferredRepaintDelay() const;
 
     void updateWidgetsTimerFired(Timer<FrameView>*);
     bool updateWidgets();
 
     void scrollToAnchor();
     void scrollPositionChanged();
+    void didScrollTimerFired(Timer<FrameView>*);
 
     bool hasCustomScrollbars() const;
     bool shouldUseCustomScrollbars(Element*& customScrollbarElement, Frame*& customScrollbarFrame);
 
     virtual void updateScrollCorner() OVERRIDE;
 
     FrameView* parentFrameView() const;
 
     AXObjectCache* axObjectCache() const;
     void removeFromAXObjectCache();
@@ skipping 104 matching lines @@
 
     bool m_hasSoftwareFilters;
 
     float m_visibleContentScaleFactor;
     IntSize m_inputEventsOffsetForEmulation;
     float m_inputEventsScaleFactorForEmulation;
 
     PartialLayoutState m_partialLayout;
     IntSize m_layoutSize;
     bool m_layoutSizeFixedToFrameSize;
+
+    Timer<FrameView> m_didScrollTimer;
 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count)
 {
     if (m_isVisuallyNonEmpty)
         return;
     m_visuallyNonEmptyCharacterCount += count;
     // Use a threshold value to prevent very small amounts of visible content from triggering didFirstVisuallyNonEmptyLayout.
     // The first few hundred characters rarely contain the interesting content of the page.
     static const unsigned visualCharacterThreshold = 200;
@@ skipping 10 matching lines @@
     static const unsigned visualPixelThreshold = 32 * 32;
     if (m_visuallyNonEmptyPixelCount > visualPixelThreshold)
         setIsVisuallyNonEmpty();
 }
 
 DEFINE_TYPE_CASTS(FrameView, Widget, widget, widget->isFrameView(), widget.isFrameView());
 
 } // namespace WebCore
 
 #endif // FrameView_h