CSS4: Implement :placeholder-shown pseudo class

Source/core/layout/LayoutTextControl.cpp

 /**
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  *           (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 59 matching lines @@
         return;
     LayoutBlock* innerEditorLayoutObject = toLayoutBlock(innerEditor->layoutObject());
     if (innerEditorLayoutObject) {
         // We may have set the width and the height in the old style in layout().
         // Reset them now to avoid getting a spurious layout hint.
         innerEditorLayoutObject->mutableStyleRef().setHeight(Length());
         innerEditorLayoutObject->mutableStyleRef().setWidth(Length());
         innerEditorLayoutObject->setStyle(createInnerEditorStyle(styleRef()));
         innerEditor->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::Control));
     }
-    textFormControlElement()->updatePlaceholderVisibility(false);
+    textFormControlElement()->updatePlaceholderVisibility();
 }
 
 static inline void updateUserModifyProperty(HTMLTextFormControlElement& node, ComputedStyle& style)
 {
     style.setUserModify(node.isDisabledOrReadOnly() ? READ_ONLY : READ_WRITE_PLAINTEXT_ONLY);
 }
 
 void LayoutTextControl::adjustInnerEditorStyle(ComputedStyle& textBlockStyle) const
 {
     // The inner block, if present, always has its direction set to LTR,
@@ skipping 201 matching lines @@
     HTMLElement* placeholder = toHTMLTextFormControlElement(node())->placeholderElement();
     LayoutObject* placeholderLayoutObject = placeholder ? placeholder->layoutObject() : nullptr;
     if (!placeholderLayoutObject)
         return nullptr;
     if (relayoutChildren)
         layoutScope.setChildNeedsLayout(placeholderLayoutObject);
     return placeholderLayoutObject;
 }
 
 } // namespace blink