Ignore attempts to navigate once a provisional commit has gotten too far along.

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 960 matching lines @@
         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)
         return;
-    if (m_documentLoader)
+    if (m_documentLoader) {
+        FrameNavigationDisabler navigationDisabler(m_frame);
         m_documentLoader->detachFromFrame();
+    }
     // detachFromFrame() will abort XHRs that haven't completed, which can
     // trigger event listeners for 'abort'. These event listeners might detach
     // the frame.
     // TODO(dcheng): Investigate if this can be moved above the check that
     // m_provisionalDocumentLoader hasn't changed.
     if (!m_frame->client())
         return;
     // No more events will be dispatched so detach the Document.
     if (m_frame->document())
         m_frame->document()->detach();
@@ skipping 452 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