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

pkg/unittest/test/middle_exception_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.middle_exception_test;
-
-import 'dart:async';
-
-import 'package:metatest/metatest.dart';
-import 'package:unittest/unittest.dart';
-
-void main() => initTests(_test);
-
-void _test(message) {
-  initMetatest(message);
-
-  expectTestResults('late exception test', () {
-    test('testOne', () {
-      expect(true, isTrue);
-    });
-    test('testTwo', () {
-      expect(true, isFalse);
-    });
-    test('testThree', () {
-      var done = expectAsync(() {});
-      new Future.sync(() {
-        expect(true, isTrue);
-        done();
-      });
-    });
-  }, [{
-    'result': 'pass'
-  }, {
-    'result': 'fail',
-  }, {
-    'result': 'pass'
-  }]);
-}