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

third_party/WebKit/Source/core/loader/FrameLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008 Alp Toker <alp@atoker.com>
  * Copyright (C) Research In Motion Limited 2009. All rights reserved.
  * Copyright (C) 2011 Kris Jordan <krisjordan@gmail.com>
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ skipping 1024 matching lines @@
         int nodeCount = static_cast<int>(totalNodeCount);
         for (Document* document : Document::liveDocumentSet()) {
             if (document != m_frame->document())
                 nodeCount -= document->nodeCount();
         }
         ASSERT(nodeCount >= 0);
         float ratio = static_cast<float>(nodeCount) / totalNodeCount;
         ThreadState::current()->schedulePageNavigationGCIfNeeded(ratio);
     }
 
+    // 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.
+    SubframeLoadingDisabler disabler(m_frame->document());
     if (m_documentLoader) {
         client()->dispatchWillClose();
         dispatchUnloadEvent();
     }
     m_frame->detachChildren();
     // The previous calls to dispatchUnloadEvent() and detachChildren() can
     // execute arbitrary script via things like unload events. If the executed
     // script intiates a new load or causes the current frame to be detached,
     // we need to abandon the current load.
     if (pdl != m_provisionalDocumentLoader)
@@ skipping 495 matching lines @@
     // FIXME: We need a way to propagate insecure requests policy flags to
     // out-of-process frames. For now, we'll always use default behavior.
     if (!parentFrame->isLocalFrame())
         return nullptr;
 
     ASSERT(toLocalFrame(parentFrame)->document());
     return toLocalFrame(parentFrame)->document()->insecureNavigationsToUpgrade();
 }
 
 } // namespace blink