Subtree caching implementation in blink-core

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 a8bb967ccd28eda6f44ecbb7bee578e7afa13204..20c02ac8e8758c35722cf6401a27a3dfd8e40fa5 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -601,6 +601,9 @@ protected:
     void invalidateTreeIfNeeded(PaintInvalidationState&);
 
 private:
+    friend class DisplayItemListPaintTestForSlimmingPaintV2;
+    friend class LayoutPart;
+
     explicit FrameView(LocalFrame*);
 
     void setScrollOffset(const IntPoint&, ScrollType) override;
@@ -609,6 +612,7 @@ private:
     enum LifeCycleUpdateOption {
         AllPhases,
         OnlyUpToCompositingCleanPlusScrolling,
+        OnlyUpToPaintForSlimmingPaintV2Clean,
     };
 
     void updateLifecyclePhasesInternal(LifeCycleUpdateOption);
@@ -626,8 +630,6 @@ private:
     // 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);