dart2js: Share nativeSuperclassTagName between runtime and compiler.

sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // 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.
 
 library _js_helper;
 
 import 'dart:_js_embedded_names' show
     ALL_CLASSES,
     GET_ISOLATE_TAG,
     INTERCEPTED_NAMES,
     INTERCEPTORS_BY_TAG,
     LEAF_TAGS,
     METADATA,
     DEFERRED_LIBRARY_URIS,
     DEFERRED_LIBRARY_HASHES,
     INITIALIZE_LOADED_HUNK,
-    IS_HUNK_LOADED;
+    IS_HUNK_LOADED,
+    NATIVE_SUPERCLASS_TAG_NAME;
 
 import 'dart:collection';
 import 'dart:_isolate_helper' show
     IsolateNatives,
     leaveJsAsync,
     enterJsAsync,
     isWorker;
 
 import 'dart:async' show Future, DeferredLoadException, Completer;
 
@@ skipping 3407 matching lines @@
   throw new MainError("No top-level function named 'main'.");
 }
 
 void badMain() {
   throw new MainError("'main' is not a function.");
 }
 
 void mainHasTooManyParameters() {
   throw new MainError("'main' expects too many parameters.");
 }