Gracefully handle nested frame detaches.

Source/core/frame/LocalFrame.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Simon Hausmann <hausmann@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  *                     2001 George Staikos <staikos@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov <ap@nypop.com>
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 252 matching lines @@
     // A lot of the following steps can result in the current frame being
     // detached, so protect a reference to it.
     RefPtrWillBeRawPtr<LocalFrame> protect(this);
     m_loader.stopAllLoaders();
     m_loader.dispatchUnloadEvent();
     detachChildren();
     // stopAllLoaders() needs to be called after detachChildren(), because detachChildren()
     // will trigger the unload event handlers of any child frames, and those event
     // handlers might start a new subresource load in this frame.
     m_loader.stopAllLoaders();
+    m_loader.detach();
     if (!client())
         return;
 
-    m_loader.detach();
     // Notify ScriptController that the frame is closing, since its cleanup ends up calling
     // back to FrameLoaderClient via WindowProxy.
     script().clearForClose();
     ScriptForbiddenScope forbidScript;
     setView(nullptr);
     willDetachFrameHost();
     InspectorInstrumentation::frameDetachedFromParent(this);
     Frame::detach();
     // Clear the FrameLoader right here rather than during
     // finalization. Too late to access various heap objects at that
@@ skipping 549 matching lines @@
     // We detach the FrameView's custom scroll bars as early as
     // possible to prevent m_doc->detach() from messing with the view
     // such that its scroll bars won't be torn down.
     //
     // FIXME: We should revisit this.
     if (m_view)
         m_view->prepareForDetach();
 }
 
 } // namespace blink