Add fast path for tag#id selector queries

Source/core/dom/TreeScope.cpp

 /*
  * Copyright (C) 2011 Google Inc. All Rights Reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 132 matching lines @@
 
 Element* TreeScope::getElementById(const AtomicString& elementId) const
 {
     if (elementId.isEmpty())
         return 0;
     if (!m_elementsById)
         return 0;
     return m_elementsById->getElementById(elementId.impl(), this);
 }
 
+const Vector<Element*>* TreeScope::getAllElementsById(const AtomicString& elementId) const
+{
+    if (elementId.isEmpty())
+        return 0;
+    if (!m_elementsById)
+        return 0;

[esprehn, 2013/12/17 18:57:48]

Why not return emptyVector? We should just add a static local I think.

[Inactive, 2013/12/17 21:20:24]

Done.

+    return m_elementsById->getAllElementsById(elementId.impl(), this);
+}
+
 void TreeScope::addElementById(const AtomicString& elementId, Element* element)
 {
     if (!m_elementsById)
         m_elementsById = adoptPtr(new DocumentOrderedMap);
     m_elementsById->add(elementId.impl(), element);
     m_idTargetObserverRegistry->notifyObservers(elementId);
 }
 
 void TreeScope::removeElementById(const AtomicString& elementId, Element* element)
 {
@@ skipping 329 matching lines @@
             result = element;
         for (ShadowRoot* shadowRoot = element->youngestShadowRoot(); shadowRoot; shadowRoot = shadowRoot->olderShadowRoot()) {
             if (Element* shadowResult = shadowRoot->getElementByAccessKey(key))
                 result = shadowResult;
         }
     }
     return result;
 }
 
 } // namespace WebCore