Don't reset LoadEventProgress if frame unload has already started.

third_party/WebKit/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 302 matching lines @@
     }
 }
 
 void LocalFrame::detach(FrameDetachType type)
 {
     PluginScriptForbiddenScope forbidPluginDestructorScripting;
     // 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();
+    // Don't allow any new child frames to load in this frame: attaching a new
+    // child frame during or after detaching children results in an attached
+    // frame on a detached DOM tree, which is bad.
+    // TODO(dcheng): Strictly speaking, this only needs to be scoped immediately
+    // before detachChildren(). However, this was previously scoped to the
+    // unload event as well. Investigate if it's possible to move it after
+    // dispatchUnloadEvent(), and if it makes sense to do that.
+    SubframeLoadingDisabler disabler(*document());
     m_loader.dispatchUnloadEvent();
     detachChildren();
     m_frameScheduler.clear();
 
     // All done if detaching the subframes brought about a detach of this frame also.
     if (!client())
         return;
 
     // stopAllLoaders() needs to be called after detachChildren(), because detachChildren()
     // will trigger the unload event handlers of any child frames, and those event
@@ skipping 573 matching lines @@
 {
     m_frame->disableNavigation();
 }
 
 FrameNavigationDisabler::~FrameNavigationDisabler()
 {
     m_frame->enableNavigation();
 }
 
 } // namespace blink