[WIP]Issue FrameDestructionObserver::frameDestroyed() notification on detach.

Source/core/frame/LocalDOMWindow.h

Index: Source/core/frame/LocalDOMWindow.h
diff --git a/Source/core/frame/LocalDOMWindow.h b/Source/core/frame/LocalDOMWindow.h
index 4ee59a6f89742b01c460db634f7a548ba67a4151..0f1fbd688339919b322eba7e5d73c603eba84cd8 100644
--- a/Source/core/frame/LocalDOMWindow.h
+++ b/Source/core/frame/LocalDOMWindow.h
@@ -236,6 +236,7 @@ private:
 
         // FrameDestructionObserver overrides:
         void willDetachFrameHost() override;
+        void frameDestroyed() override;
 
         RawPtrWillBeMember<LocalDOMWindow> m_window;
     };
@@ -259,6 +260,7 @@ private:
     };
 
     void willDetachFrameHost();
+    void frameDestroyed();
     void removeAllEventListenersInternal(BroadcastListenerRemoval);
 
     OwnPtrWillBeMember<WindowFrameObserver> m_frameObserver;