Partially rollback noSuchMethod for UnknownElement until we figure out code size issue

lib/dom/templates/html/impl/impl_UnknownElement.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.
 
 // Temporary dispatch hook to support WebComponents.
 Function dynamicUnknownElementDispatcher;
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
 
   // Hooks to support custom WebComponents.
   var xtag;
 
+$if DARTIUM
   noSuchMethod(String name, List args) {
     if (dynamicUnknownElementDispatcher == null) {
       throw new NoSuchMethodException(this, name, args);
     } else {
       return dynamicUnknownElementDispatcher(this, name, args);
     }
   }
+$else
+  // TODO(vsm): Implement noSuchMethod or similar for dart2js.
+$endif
 }