Subtree caching implementation in blink-core

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 584 matching lines @@
             : m_scope(view->m_inUpdateScrollbars, true)
         { }
     private:
         TemporaryChange<bool> m_scope;
     };
 
     // Only for LayoutPart to traverse into sub frames during paint invalidation.
     void invalidateTreeIfNeeded(PaintInvalidationState&);
 
 private:
+    friend class DisplayItemListPaintTestForSlimmingPaintV2;
+    friend class LayoutPart;
+
     explicit FrameView(LocalFrame*);
 
     void setScrollOffset(const IntPoint&, ScrollType) override;
     void setScrollOffset(const DoublePoint&, ScrollType) override;
 
     enum LifeCycleUpdateOption {
         AllPhases,
         OnlyUpToCompositingCleanPlusScrolling,
+        OnlyUpToPaintForSlimmingPaintV2Clean,
     };
 
     void updateLifecyclePhasesInternal(LifeCycleUpdateOption);
     void invalidateTreeIfNeededRecursive();
     void scrollContentsIfNeededRecursive();
     void updateStyleAndLayoutIfNeededRecursive();
     void paintForSlimmingPaintV2();
     void compositeForSlimmingPaintV2();
 
     void reset();
     void init();
 
     void clearLayoutSubtreeRootsAndMarkContainingBlocks();
 
     // Called when our frame rect changes (or the rect/scroll position of an ancestor changes).
     void frameRectsChanged() override;
 
-    friend class LayoutPart;
-
     bool contentsInCompositedLayer() const;
 
     void applyOverflowToViewport(LayoutObject*, ScrollbarMode& hMode, ScrollbarMode& vMode);
 
     void updateCounters();
     void forceLayoutParentViewIfNeeded();
     void performPreLayoutTasks();
     void performLayout(bool inSubtreeLayout);
     void scheduleOrPerformPostLayoutTasks();
     void performPostLayoutTasks();
@@ skipping 222 matching lines @@
     static const unsigned visualPixelThreshold = 32 * 32;
     if (m_visuallyNonEmptyPixelCount > visualPixelThreshold)
         setIsVisuallyNonEmpty();
 }
 
 DEFINE_TYPE_CASTS(FrameView, Widget, widget, widget->isFrameView(), widget.isFrameView());
 
 } // namespace blink
 
 #endif // FrameView_h