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 2b927493980b7533a852fb49cf5caf9c8f46bd55..a1b2b4383ff62b44434aa193bdc964110947d04a 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -77,10 +77,13 @@ typedef unsigned long long DOMTimeStamp;
 
 class CORE_EXPORT FrameView final : public Widget, public ScrollableArea {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(FrameView);
-public:
-    friend class LayoutView;
+
+    friend class DisplayItemListPaintTestForSlimmingPaintV2;
     friend class Internals;
+    friend class LayoutPart; // for invalidateTreeIfNeeded
+    friend class LayoutView; // for contentRectangleForPaintInvalidation
 
+public:
     static PassRefPtrWillBeRawPtr<FrameView> create(LocalFrame*);
     static PassRefPtrWillBeRawPtr<FrameView> create(LocalFrame*, const IntSize& initialSize);
 
@@ -624,8 +627,6 @@ 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);