Deal with the JS helper separately from the 'native' keyword.

pkg/dartdoc/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('../../../lib/compiler/compiler.dart', prefix: 'diagnostics');
 #import('../../../lib/compiler/implementation/elements/elements.dart');
 #import('../../../lib/compiler/implementation/apiimpl.dart', prefix: 'api');
 #import('../../../lib/compiler/implementation/scanner/scannerlib.dart');
@@ skipping 203 matching lines @@
     log('compilation succeeded');
     return true;
   }
 
   void runCompilerList(List<Uri> uriList) {
     scanBuiltinLibraries();
     var elementList = <LibraryElement>[];
     for (var uri in uriList) {
       elementList.add(scanner.loadLibrary(uri, null, uri));
     }
+    libraries.forEach((_, library) {
+      maybeEnableJSHelper(library);
+    });
 
     world.populate(this);
 
     log('Resolving...');
     phase = Compiler.PHASE_RESOLVING;
     backend.enqueueHelpers(enqueuer.resolution);
     processQueueList(enqueuer.resolution, elementList);
     log('Resolved ${enqueuer.resolution.resolvedElements.length} elements.');
   }
 
@@ skipping 1134 matching lines @@
     if (node !== null) {
       var span = system.compiler.spanFromNode(node, script.uri);
       return new Dart2JsLocation(script, span);
     } else {
       var span = system.compiler.spanFromElement(_variable);
       return new Dart2JsLocation(script, span);
     }
   }
 }