Use @Native annotation on dart2js DOM native classes

tools/dom/templates/html/dart2js/impl_RTCSessionDescription.darttemplate

 // Copyright (c) 2013, 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;
 
-$(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+$(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
   factory $CLASSNAME(Map dictionary) {
     // TODO(efortuna): Remove this check if when you can actually construct with
     // the unprefixed RTCIceCandidate in Firefox (currently both are defined,
     // but one can't be used as a constructor).
     var constructorName = JS('', 'window[#]',
         Device.isFirefox ? '${Device.propertyPrefix}RTCSessionDescription' :
        'RTCSessionDescription');
     return JS('RtcSessionDescription',
         'new #(#)', constructorName,
         convertDartToNative_SerializedScriptValue(dictionary));
   }
 $!MEMBERS
 }