Implement ::placeholder CSS selector.

third_party/WebKit/Source/core/css/SelectorChecker.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 1049 matching lines @@
 
       for (subContext.selector = selector.selectorList()->first();
            subContext.selector;
            subContext.selector = CSSSelectorList::next(*subContext.selector)) {
         if (match(subContext))
           return true;
       }
       return false;
     }
     case CSSSelector::PseudoWebKitCustomElement: {
-      if (ShadowRoot* root = element.containingShadowRoot())
-        return root->type() == ShadowRootType::UserAgent &&
-               element.shadowPseudoId() == selector.value();
+      if (ShadowRoot* root = element.containingShadowRoot()) {
+        if (root->type() != ShadowRootType::UserAgent)
+          return false;
+        const AtomicString& pseudoName = element.shadowPseudoId();
+        if (pseudoName == selector.value())
+          return true;
+        AtomicString alias = CSSSelector::aliasForShadowPseudoId(pseudoName);
+        return !alias.isEmpty() && alias == selector.value();
+      }
       return false;
     }
     case CSSSelector::PseudoBlinkInternalElement:
       if (!m_isUARule)
         return false;
       if (ShadowRoot* root = element.containingShadowRoot())
         return root->type() == ShadowRootType::UserAgent &&
                element.shadowPseudoId() == selector.value();
       return false;
     case CSSSelector::PseudoSlotted: {
@@ skipping 194 matching lines @@
 }
 
 bool SelectorChecker::matchesFocusPseudoClass(const Element& element) {
   if (InspectorInstrumentation::forcePseudoState(const_cast<Element*>(&element),
                                                  CSSSelector::PseudoFocus))
     return true;
   return element.isFocused() && isFrameFocused(element);
 }
 
 }  // namespace blink