Migrate test block 47 and downstream dependencies to Dart 2.0.

tests/language/checked_mode_helper.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 checked_mode_helper;
-
-import 'package:expect/expect.dart';
-
-/// Returns `true` if the program is running in checked mode.
-bool inCheckedMode() {
-  try {
-    var i = 42;
-    String s = i;
-  } on TypeError catch (e) {
-    return true;
-  }
-  return false;
-}
-
-/// Checks that a dynamic type error is thrown if and only if [f] is executed in
-/// checked mode and [expectTypeError] is `true`.
-void testDynamicTypeError(bool expectTypeError, f(), [String message]) {
-  if (expectTypeError) {
-    checkDynamicTypeError(f, message);
-  } else {
-    checkNoDynamicTypeError(f, message);
-  }
-}
-
-/// Checks that a dynamic type error is thrown if and only if [f] is executed in
-/// checked mode.
-void checkDynamicTypeError(f(), [String message]) {
-  message = message != null ? ': $message' : '';
-  try {
-    f();
-    Expect.isFalse(
-        inCheckedMode(), 'Missing type error in checked mode$message.');
-  } on TypeError catch (e) {
-    Expect.isTrue(inCheckedMode(), 'Unexpected type error in production mode.');
-  }
-}
-
-/// Checks that no dynamic type error is thrown when [f] is executed regardless
-/// of execution mode.
-void checkNoDynamicTypeError(f(), [String message]) {
-  message = message != null ? ': $message' : '';
-  try {
-    f();
-  } on TypeError catch (e) {
-    String mode = inCheckedMode() ? 'checked mode' : 'production mode';
-    Expect.fail('Unexpected type error in $mode$message.');
-  }
-}