Make dart2js unittests async.

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 30 matching lines @@
     scanner = new TestScanner(this);
     resolver = new TestResolver(this, backend.constantCompilerTask);
     test('Compiler');
   }
 
   Future<bool> run(Uri uri) {
     test('Compiler.run');
     return super.run(uri);
   }
 
-  Future scanBuiltinLibraries() {
+  /*Future scanBuiltinLibraries() {

[karlklose, 2014/06/10 12:32:54]

Remove the code?

     test('Compiler.scanBuiltinLibraries');
     return super.scanBuiltinLibraries();
-  }
+  }*/
 
   void initializeSpecialClasses() {
     test('Compiler.initializeSpecialClasses');
     super.initializeSpecialClasses();
   }
 
   TreeElements analyzeElement(Element element) {
     test('Compiler.analyzeElement');
     return super.analyzeElement(element);
   }
@@ skipping 176 matching lines @@
     'invariant': 253,
     'warning': 0,
     'error': 1,
     'fatalError': 1,
     'internalError': 253,
   };
 
   final tests = {
     'Compiler': beforeRun,
     'Compiler.run': beforeRun,
-    'Compiler.scanBuiltinLibraries': beforeRun,
+    //'Compiler.scanBuiltinLibraries': beforeRun,
     'Compiler.initializeSpecialClasses': beforeRun,
     'ScannerTask.scanElements': duringRun,
     'Compiler.withCurrentElement': duringRun,
     'Compiler.analyzeElement': duringRun,
     'Compiler.codegen': duringRun,
     'ResolverTask.computeClassMembers': duringRun,
   };
 
   asyncStart();
   Future.forEach(tests.keys, (marker) {
     return testExitCodes(marker, tests[marker]);
   }).then((_) {
     int countResults(Map runType) {
       return runType.length *
              tests.values.where((r) => r == runType).length;
     }
 
     Expect.equals(countResults(beforeRun) + countResults(duringRun),
                   checkedResults);
     asyncEnd();
   });
 }