Add a counter and a deprecation message when navigating in an unload handler.

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 92 matching lines @@
     {
         ASSERT(s_navigationDisableCount);
         s_navigationDisableCount--;
     }
     static bool isNavigationAllowed() { return !s_navigationDisableCount; }
 
 private:
     static unsigned s_navigationDisableCount;
 };
 
+class CORE_EXPORT NavigationCounterForUnload {
+    WTF_MAKE_NONCOPYABLE(NavigationCounterForUnload);
+    STACK_ALLOCATED();
+public:
+    NavigationCounterForUnload()
+    {
+        s_inUnloadHandler++;
+    }
+    ~NavigationCounterForUnload()
+    {
+        DCHECK(s_inUnloadHandler);
+        s_inUnloadHandler--;
+    }
+    static bool inUnloadHandler() { return !!s_inUnloadHandler; }
+
+private:
+    static unsigned s_inUnloadHandler;
+};
+
 } // namespace blink
 
 #endif // NavigationScheduler_h