Revert "Reverting custom pseudo element".

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1016 matching lines @@
         AtomicString oldId = elementData()->idForStyleResolution();
         AtomicString newId = makeIdForStyleResolution(newValue, document().inQuirksMode());
         if (newId != oldId) {
             elementData()->setIdForStyleResolution(newId);
             shouldInvalidateStyle = testShouldInvalidateStyle && checkNeedsStyleInvalidationForIdChange(oldId, newId, styleResolver->ensureRuleFeatureSet());
         }
     } else if (name == classAttr) {
         classAttributeChanged(newValue);
     } else if (name == HTMLNames::nameAttr) {
         setHasName(!newValue.isNull());
+    } else if (name == HTMLNames::pseudoAttr) {
+        shouldInvalidateStyle |= testShouldInvalidateStyle && isInShadowTree();
     }
 
     invalidateNodeListCachesInAncestors(&name, this);
 
     // If there is currently no StyleResolver, we can't be sure that this attribute change won't affect style.
     shouldInvalidateStyle |= !styleResolver;
 
     if (shouldInvalidateStyle)
         setNeedsStyleRecalc(SubtreeStyleChange);
 
@@ skipping 1381 matching lines @@
             continue;
         content.append(toText(child)->data());
     }
 
     ASSERT(content.length() == totalLength);
     return content.toString();
 }
 
 const AtomicString& Element::shadowPseudoId() const
 {
-    if (ShadowRoot* root = containingShadowRoot()) {
-        if (root->type() == ShadowRoot::UserAgentShadowRoot)
-            return fastGetAttribute(pseudoAttr);
-    }
-    return nullAtom;
+    return getAttribute(pseudoAttr);
 }
 
 void Element::setShadowPseudoId(const AtomicString& id)
 {
-    ASSERT(CSSSelector::parsePseudoType(id) == CSSSelector::PseudoWebKitCustomElement || CSSSelector::parsePseudoType(id) == CSSSelector::PseudoUserAgentCustomElement);
     setAttribute(pseudoAttr, id);
 }
 
 bool Element::isInDescendantTreeOf(const Element* shadowHost) const
 {
     ASSERT(shadowHost);
     ASSERT(isShadowHost(shadowHost));
 
     const ShadowRoot* shadowRoot = containingShadowRoot();
     while (shadowRoot) {
@@ skipping 1082 matching lines @@
     // Before doing so, we need to resolve issues in HTMLSelectElement::recalcListItems
     // and RenderMenuList::setText. See also https://bugs.webkit.org/show_bug.cgi?id=88405
     if (hasTagName(optionTag) || hasTagName(optgroupTag))
         return false;
     if (FullscreenElementStack::isActiveFullScreenElement(this))
         return false;
     return true;
 }
 
 } // namespace WebCore