Move isNavigationAllowed() check to main entry point for loads.

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010 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) 2009 Adam Barth. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
@@ skipping 261 matching lines @@
 bool NavigationScheduler::locationChangePending()
 {
     return m_redirect && m_redirect->isLocationChange();
 }
 
 bool NavigationScheduler::isNavigationScheduled() const
 {
     return m_redirect;
 }
 
+// TODO(dcheng): There are really two different load blocking concepts at work
+// here and they have been incorrectly tangled together.
+//
+// 1. NavigationDisablerForBeforeUnload is for blocking navigation scheduling
+//    during a beforeunload event. Scheduled navigations during beforeunload
+//    would make it possible to get trapped in an endless loop of beforeunload
+//    dialogs.
+//
+//    Checking Frame::isNavigationAllowed() doesn't make sense in this context:
+//    NavigationScheduler is always cleared when a new load commits, so it's
+//    impossible for a scheduled navigation to clobber a navigation that just
+//    committed.
+//
+// 2. FrameNavigationDisabler / LocalFrame::isNavigationAllowed() are intended
+//    to prevent Documents from being reattached during destruction, since it
+//    can cause bugs with security origin confusion. This is primarily intended
+//    to block /synchronous/ navigations during things lke Document::detach().
 inline bool NavigationScheduler::shouldScheduleReload() const
 {
     return m_frame->page() && m_frame->isNavigationAllowed() && NavigationDisablerForBeforeUnload::isNavigationAllowed();
 }
 
 inline bool NavigationScheduler::shouldScheduleNavigation(const String& url) const
 {
     return m_frame->page() && m_frame->isNavigationAllowed() && (protocolIsJavaScript(url) || NavigationDisablerForBeforeUnload::isNavigationAllowed());
 }
 
@@ skipping 140 matching lines @@
     m_redirect.clear();
 }
 
 DEFINE_TRACE(NavigationScheduler)
 {
     visitor->trace(m_frame);
     visitor->trace(m_redirect);
 }
 
 } // namespace blink