Refactor ResourceLoadPriorityOptimizer to avoid walking render tree

Source/core/frame/FrameView.h

Index: Source/core/frame/FrameView.h
diff --git a/Source/core/frame/FrameView.h b/Source/core/frame/FrameView.h
index 5cad0ffd0f641d3dd12179b6c3beb37bcd44635a..7a660123dd65988e9174eeb72b2937aa268bff76 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -434,6 +434,7 @@ private:
 
     void scrollToAnchor();
     void scrollPositionChanged();
+    void didScrollTimerFired(Timer<FrameView>*);
 
     bool hasCustomScrollbars() const;
     bool shouldUseCustomScrollbars(Element*& customScrollbarElement, Frame*& customScrollbarFrame);
@@ -558,6 +559,8 @@ private:
     PartialLayoutState m_partialLayout;
     IntSize m_layoutSize;
     bool m_layoutSizeFixedToFrameSize;
+
+    Timer<FrameView> m_didScrollTimer;
 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count)