CSS4: Implement :placeholder-shown pseudo class

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 241 matching lines @@
     bool supportsInputModeAttribute() const;
 
     void setShouldRevealPassword(bool value);
     bool shouldRevealPassword() const { return m_shouldRevealPassword; }
     AXObject* popupRootAXObject();
     void didNotifySubtreeInsertionsToDocument() override;
 
     virtual void ensureFallbackContent();
     virtual void ensurePrimaryContent();
     bool hasFallbackContent() const;
+
+    bool isPlaceholderVisible() const override { return m_isPlaceholderVisible; }
+    void setPlaceholderVisibility(bool) override;
+
 protected:
     HTMLInputElement(Document&, HTMLFormElement*, bool createdByParser);
 
     void defaultEventHandler(Event*) override;
 
 private:
     enum AutoCompleteSetting { Uninitialized, On, Off };
 
     void didAddUserAgentShadowRoot(ShadowRoot&) final;
     void willAddFirstAuthorShadowRoot() final;
@@ skipping 105 matching lines @@
     unsigned m_isActivatedSubmit : 1;
     unsigned m_autocomplete : 2; // AutoCompleteSetting
     unsigned m_hasNonEmptyList : 1;
     unsigned m_stateRestored : 1;
     unsigned m_parsingInProgress : 1;
     unsigned m_valueAttributeWasUpdatedAfterParsing : 1;
     unsigned m_canReceiveDroppedFiles : 1;
     unsigned m_hasTouchEventHandler : 1;
     unsigned m_shouldRevealPassword : 1;
     unsigned m_needsToUpdateViewValue : 1;
+    unsigned m_isPlaceholderVisible : 1;
     RefPtrWillBeMember<InputType> m_inputType;
     RefPtrWillBeMember<InputTypeView> m_inputTypeView;
     // 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