Migrated test block 168 to Dart 2.0.

tests/lib_strong/async/future_constructor_test.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 future_test;
-
-import "package:expect/expect.dart";
-import 'dart:async';
-
-main() {
-  compare(func) {
-    // Compare the results of the following two futures.
-    Future f1 = new Future(func);
-    Future f2 = new Future.value().then((_) => func());
-    f2.catchError((_) {}); // I'll get the error later.
-    f1.then((v1) {
-      f2.then((v2) {
-        Expect.equals(v1, v2);
-      });
-    }, onError: (e1) {
-      f2.then((_) {
-        Expect.fail("Expected error");
-      }, onError: (e2) {
-        Expect.equals(e1, e2);
-      });
-    });
-  }
-
-  Future val = new Future.value(42);
-  Future err1 = new Future.error("Error")..catchError((_) {});
-  compare(() => 42);
-  compare(() => val);
-  compare(() {
-    throw "Flif";
-  });
-  compare(() => err1);
-  bool hasExecuted = false;
-  compare(() {
-    hasExecuted = true;
-    return 499;
-  });
-  Expect.isFalse(hasExecuted);
-}