Use Shadow DOM to display fallback content for images

Source/core/html/HTMLInputElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 158 matching lines @@
     virtual RenderObject* createRenderer(RenderStyle*) OVERRIDE;
     virtual void detach(const AttachContext& = AttachContext()) OVERRIDE FINAL;
     virtual void updateFocusAppearance(bool restorePreviousSelection) OVERRIDE FINAL;
 
     // FIXME: For isActivatedSubmit and setActivatedSubmit, we should use the NVI-idiom here by making
     // it private virtual in all classes and expose a public method in HTMLFormControlElement to call
     // the private virtual method.
     virtual bool isActivatedSubmit() const OVERRIDE FINAL;
     virtual void setActivatedSubmit(bool flag) OVERRIDE FINAL;
 
-    String altText() const;
+    virtual String altText() const OVERRIDE FINAL;
 
     int maxResults() const { return m_maxResults; }
 
     const AtomicString& defaultValue() const;
 
     Vector<String> acceptMIMETypes();
     Vector<String> acceptFileExtensions();
     const AtomicString& alt() const;
 
     void setSize(unsigned);
@@ skipping 74 matching lines @@
 
     bool setupDateTimeChooserParameters(DateTimeChooserParameters&);
 
     bool supportsInputModeAttribute() const;
 
     void setShouldRevealPassword(bool value);
     bool shouldRevealPassword() const { return m_shouldRevealPassword; }
     AXObject* popupRootAXObject();
     virtual void didNotifySubtreeInsertionsToDocument() OVERRIDE;
 
+    virtual void ensureFallbackContent() OVERRIDE FINAL;
+    virtual void ensurePrimaryContent() OVERRIDE FINAL;
 protected:
     HTMLInputElement(Document&, HTMLFormElement*, bool createdByParser);
 
     virtual void defaultEventHandler(Event*) OVERRIDE;
 
 private:
     enum AutoCompleteSetting { Uninitialized, On, Off };
 
     virtual void didAddUserAgentShadowRoot(ShadowRoot&) OVERRIDE FINAL;
     virtual void willAddFirstAuthorShadowRoot() OVERRIDE FINAL;
@@ skipping 111 matching lines @@
     // The ImageLoader must be owned by this element because the loader code assumes
     // that it lives as long as its owning element lives. If we move the loader into
     // the ImageInput object we may delete the loader while this element lives on.
     OwnPtrWillBeMember<HTMLImageLoader> m_imageLoader;
     OwnPtrWillBeMember<ListAttributeTargetObserver> m_listAttributeTargetObserver;
 };
 
 } // namespace blink
 
 #endif // HTMLInputElement_h