Use @Native annotation on dart2js DOM native classes

tools/dom/templates/html/impl/impl_WebKitCSSKeyframesRule.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.
 
 part of $LIBRARYNAME;
 
 @DocsEditable()
-$(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$MIXINS$IMPLEMENTS$NATIVESPEC {
+$(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$MIXINS$IMPLEMENTS {
 $!MEMBERS
 
 $if DART2JS
   void appendRule(String rule) {
     if (JS('bool', '("appendRule" in #)', this)) {
       JS('', '#.appendRule(#)', this, rule);
     } else {
       JS('', '#.insertRule(#)', this, rule);
     }
   }
 $endif
 }