Private libraries used.

sdk/lib/_internal/compiler/implementation/mirrors/dart2js_mirror.dart

 // 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.
 
 library mirrors_dart2js;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:uri';
 
@@ skipping 270 matching lines @@
     log('compilation succeeded');
     return true;
   }
 
   void runCompilerList(List<Uri> uriList) {
     scanBuiltinLibraries();
     var elementList = <LibraryElement>[];
     for (var uri in uriList) {
       elementList.add(libraryLoader.loadLibrary(uri, null, uri));
     }
-    libraries.forEach((_, library) {
-      maybeEnableJSHelper(library);
-    });
 
     world.populate();
 
     log('Resolving...');
     phase = Compiler.PHASE_RESOLVING;
     backend.enqueueHelpers(enqueuer.resolution);
     processQueueList(enqueuer.resolution, elementList);
     log('Resolved ${enqueuer.resolution.resolvedElements.length} elements.');
   }
 
@@ skipping 1556 matching lines @@
       return new Future.immediate(
           new Dart2JsStringConstantMirror.fromString(mirrors, text));
     } else if (fieldName == 'trimmedText') {
       return new Future.immediate(
           new Dart2JsStringConstantMirror.fromString(mirrors, trimmedText));
     }
     // TODO(johnniwinther): Which exception/error should be thrown here?
     throw new UnsupportedError('InstanceMirror does not have a reflectee');
   }
 }