Emit warning on import of dart:mirrors.

tests/compiler/dart2js/exit_code_test.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.
 
 // Test the exit code of dart2js in case of exceptions, fatal errors, errors,
 // warnings, etc.
 
 
 import 'dart:async';
 import 'dart:io' show Platform;
@@ skipping 36 matching lines @@
   Future<bool> run(Uri uri) {
     test('Compiler.run');
     return super.run(uri);
   }
 
   Future onLibraryScanned(LibraryElement element, LibraryLoader loader) {
     test('Compiler.onLibraryScanned');
     return super.onLibraryScanned(element, loader);
   }
 
-  Future onLibrariesLoaded(Map<Uri, LibraryElement> loadedLibraries) {
+  Future onLibrariesLoaded(LoadedLibraries loadedLibraries) {
     test('Compiler.onLibrariesLoaded');
     return super.onLibrariesLoaded(loadedLibraries);
   }
 
   void analyzeElement(Element element) {
     test('Compiler.analyzeElement');
     super.analyzeElement(element);
   }
 
   void codegen(CodegenWorkItem work, CodegenEnqueuer world) {
@@ skipping 197 matching lines @@
     int countResults(Map runType) {
       return runType.length *
              tests.values.where((r) => r == runType).length;
     }
 
     Expect.equals(countResults(beforeRun) + countResults(duringRun),
                   checkedResults);
     asyncEnd();
   });
 }