Form validation: Validation bubble should be closed on document unload process.

third_party/WebKit/Source/web/ValidationMessageClientImpl.h

 /*
  * Copyright (C) 2012 Google Inc. 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
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 42 matching lines @@
   void checkAnchorStatus(TimerBase*);
   FrameView* currentView();
 
   void showValidationMessage(const Element& anchor,
                              const String& message,
                              TextDirection messageDir,
                              const String& subMessage,
                              TextDirection subMessageDir) override;
   void hideValidationMessage(const Element& anchor) override;
   bool isValidationMessageVisible(const Element& anchor) override;
+  void willUnloadDocument(const Document&) override;
   void documentDetached(const Document&) override;
   void willBeDestroyed() override;
 
   WebViewImpl& m_webView;
   Member<const Element> m_currentAnchor;
   String m_message;
   IntRect m_lastAnchorRectInScreen;
   float m_lastPageScaleFactor;
   double m_finishTime;
   std::unique_ptr<TimerBase> m_timer;
 };
 
 }  // namespace blink
 
 #endif