Fix typo in dartium query selector code.

lib/dom/templates/html/impl/impl_Document.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class $CLASSNAME extends _NodeImpl
     implements Document
 $if FROG
     native "*HTMLDocument"
 $endif
     {
 
 $!MEMBERS
   // TODO(jacobr): implement all Element methods not on Document. 
 
   _ElementImpl query(String selectors) {
     // It is fine for our RegExp to detect element id query selectors to have
     // false negatives but not false positives.
     if (const RegExp("^#[_a-zA-Z]\\w*\$").hasMatch(selectors)) {
       return $dom_getElementById(selectors.substring(1));
     }
     return $dom_querySelector(selectors);
   }
 
 // TODO(jacobr): autogenerate this method.
 $if FROG
   _ElementImpl $dom_querySelector(String selectors) native "return this.querySelector(selectors);";
 $else
   _ElementImpl $dom_querySelector(String selectors) =>
-      _wrap(_.querySelector(selectors));
+      _wrap(_ptr.querySelector(selectors));
 $endif
 
   ElementList queryAll(String selectors) {
     if (const RegExp("""^\\[name=["'][^'"]+['"]\\]\$""").hasMatch(selectors)) {
       final mutableMatches = $dom_getElementsByName(
           selectors.substring(7,selectors.length - 2));
       int len = mutableMatches.length;
       final copyOfMatches = new List<Element>(len);
       for (int i = 0; i < len; ++i) {
         copyOfMatches[i] = mutableMatches[i];
       }
       return new _FrozenElementList._wrap(copyOfMatches);
     } else if (const RegExp("^[*a-zA-Z0-9]+\$").hasMatch(selectors)) {
       final mutableMatches = $dom_getElementsByTagName(selectors);
       int len = mutableMatches.length;
       final copyOfMatches = new List<Element>(len);
       for (int i = 0; i < len; ++i) {
         copyOfMatches[i] = mutableMatches[i];
       }
       return new _FrozenElementList._wrap(copyOfMatches);
     } else {
       return new _FrozenElementList._wrap($dom_querySelectorAll(selectors));
     }
   }
 }