Make dartj2s do type conversions on constructor arguments

tools/dom/templates/html/impl/impl_Notification.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;
 
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 
   factory $CLASSNAME(String title, {String dir: null, String body: null,
       String lang: null, String tag: null, String icon: null}) {
 
     var parsedOptions = {};
     if (dir != null) parsedOptions['dir'] = dir;
     if (body != null) parsedOptions['body'] = body;
     if (lang != null) parsedOptions['lang'] = lang;
     if (tag != null) parsedOptions['tag'] = tag;
     if (icon != null) parsedOptions['icon'] = icon;
-    var nativeOptions;
-$if DART2JS
-    nativeOptions = convertDartToNative_Dictionary(parsedOptions);
-$else
-    nativeOptions = parsedOptions;
-$endif
-    return $CLASSNAME._factory$CLASSNAME(title, nativeOptions);
+    return $CLASSNAME._factory$CLASSNAME(title, parsedOptions);
   }
 $!MEMBERS
 }