Allow expensive task blocking if there is pending iframe navigation

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
@@ skipping 69 matching lines @@
     bool shouldScheduleNavigation(const String& url) const;
 
     void navigateTask();
     void schedule(ScheduledNavigation*);
 
     static bool mustReplaceCurrentItem(LocalFrame* targetFrame);
 
     Member<LocalFrame> m_frame;
     OwnPtr<CancellableTaskFactory> m_navigateTaskFactory;
     Member<ScheduledNavigation> m_redirect;
+    bool m_frameIsMainFrame; // Exists because we can't deref m_frame in destructor.
 };
 
 class NavigationDisablerForBeforeUnload {
     WTF_MAKE_NONCOPYABLE(NavigationDisablerForBeforeUnload);
     STACK_ALLOCATED();
 public:
     NavigationDisablerForBeforeUnload()
     {
         s_navigationDisableCount++;
     }
     ~NavigationDisablerForBeforeUnload()
     {
         ASSERT(s_navigationDisableCount);
         s_navigationDisableCount--;
     }
     static bool isNavigationAllowed() { return !s_navigationDisableCount; }
 
 private:
     static unsigned s_navigationDisableCount;
 };
 
 } // namespace blink
 
 #endif // NavigationScheduler_h