Revert of Issue FrameDestructionObserver::frameDestroyed() notification on detach.

Source/core/frame/LocalFrame.cpp

Index: Source/core/frame/LocalFrame.cpp
diff --git a/Source/core/frame/LocalFrame.cpp b/Source/core/frame/LocalFrame.cpp
index a26e93efdc70c55ceac931965c7913172a1ece68..59c68fb30f1656f1e87a4186e7e690d9dae676e4 100644
--- a/Source/core/frame/LocalFrame.cpp
+++ b/Source/core/frame/LocalFrame.cpp
@@ -206,7 +206,15 @@
 #if !ENABLE(OILPAN)
     // Oilpan: see setDOMWindow() comment why it is acceptable not to
     // mirror the non-Oilpan call below.
+    //
+    // Also, FrameDestructionObservers that live longer than this
+    // frame object keep weak references to the frame; those will be
+    // automatically cleared by the garbage collector. Hence, explicit
+    // frameDestroyed() notifications aren't needed.
     setDOMWindow(nullptr);
+
+    for (const auto& frameDestructionObserver : m_destructionObservers)
+        frameDestructionObserver->frameDestroyed();
 #endif
 }
 
@@ -283,11 +291,6 @@
     // finalization. Too late to access various heap objects at that
     // stage.
     m_loader.clear();
-
-    // Signal frame destruction here rather than in the destructor.
-    // Main motivation is to avoid being dependent on its exact timing (Oilpan.)
-    for (const auto& frameDestructionObserver : m_destructionObservers)
-        frameDestructionObserver->frameDestroyed();
 }
 
 SecurityContext* LocalFrame::securityContext() const