Re-apply "Remove unittest and matcher from the repo."

pkg/unittest/test/excess_callback_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.
-
-library unittest.excess_callback_test;
-
-import 'dart:async';
-
-import 'package:metatest/metatest.dart';
-import 'package:unittest/unittest.dart';
-
-void main() => initTests(_test);
-
-void _test(message) {
-  initMetatest(message);
-
-  var count = 0;
-
-  expectTestResults('excess callback test', () {
-    test('test', () {
-      var _callback0 = expectAsync(() => ++count);
-      var _callback1 = expectAsync(() => ++count);
-      var _callback2 = expectAsync(() {
-        _callback1();
-        _callback1();
-        _callback0();
-      });
-      new Future.sync(_callback2);
-    });
-
-    test('verify count', () {
-      expect(count, 1);
-    });
-  }, [{
-    'description': 'test',
-    'message': 'Callback called more times than expected (1).',
-    'result': 'fail'
-  }, {
-    'description': 'verify count',
-    'result': 'pass',
-  }]);
-}