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 658e9df69d0958472e573808d1a75d3d7163a007..cb0a2ac4159c9e4a0c07c09687923e1f3ee9612e 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -602,6 +602,9 @@ protected:
     void invalidateTreeIfNeeded(PaintInvalidationState&);
 
 private:
+    friend class DisplayItemListPaintTestForSlimmingPaintV2;
+    friend class LayoutPart;
+
     explicit FrameView(LocalFrame*);
 
     void setScrollOffset(const IntPoint&, ScrollType) override;
@@ -610,6 +613,7 @@ private:
     enum LifeCycleUpdateOption {
         AllPhases,
         OnlyUpToCompositingCleanPlusScrolling,
+        OnlyUpToPaintForSlimmingPaintV2Clean,
     };
 
     void updateLifecyclePhasesInternal(LifeCycleUpdateOption);
@@ -627,8 +631,6 @@ 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);