Make Element::attributes() less error-prone and simplify call sites

Source/core/css/SelectorChecker.h

 /*
  * 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/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 147 matching lines @@
         return true;
     const AtomicString& localName = tagQName.localName();
     if (localName != starAtom && localName != element.localName())
         return false;
     const AtomicString& namespaceURI = tagQName.namespaceURI();
     return namespaceURI == starAtom || namespaceURI == element.namespaceURI();
 }
 
 inline bool SelectorChecker::checkExactAttribute(const Element& element, const QualifiedName& selectorAttributeName, const StringImpl* value)
 {
-    if (!element.hasAttributesWithoutUpdate())
-        return false;
-    AttributeCollection attributes = element.attributes();
+    AttributeCollection attributes = element.attributesWithoutUpdate();
     AttributeCollection::const_iterator end = attributes.end();
     for (AttributeCollection::const_iterator it = attributes.begin(); it != end; ++it) {
         if (it->matches(selectorAttributeName) && (!value || it->value().impl() == value))
             return true;
     }
     return false;
 }
 
 inline bool SelectorChecker::isHostInItsShadowTree(const Element& element, const ContainerNode* scope)
 {
     return scope && scope->isInShadowTree() && scope->shadowHost() == element;
 }
 
 }
 
 #endif