Migrate test block 10 to Dart 2.0.

tests/corelib_strong/iterable_element_at_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.
-
-import "package:expect/expect.dart";
-
-main() {
-  List<int> list1 = <int>[1, 2, 3];
-  List<int> list2 = const <int>[4, 5, 6];
-  List<String> list3 = <String>[];
-  Set<int> set1 = new Set<int>();
-  set1..add(11)..add(12)..add(13);
-  Set set2 = new Set();
-
-  Expect.equals(1, list1.elementAt(0));
-  Expect.equals(2, list1.elementAt(1));
-  Expect.equals(3, list1.elementAt(2));
-  Expect.throws(
-      () => list1.elementAt("2"), (e) => e is ArgumentError || e is TypeError);
-  Expect.throws(() => list1.elementAt(-1), (e) => e is ArgumentError);
-  Expect.throws(() => list1.elementAt(3), (e) => e is RangeError);
-
-  Expect.equals(4, list2.elementAt(0));
-  Expect.equals(5, list2.elementAt(1));
-  Expect.equals(6, list2.elementAt(2));
-  Expect.throws(
-      () => list2.elementAt("2"), (e) => e is ArgumentError || e is TypeError);
-  Expect.throws(() => list2.elementAt(-1), (e) => e is ArgumentError);
-  Expect.throws(() => list2.elementAt(3), (e) => e is RangeError);
-
-  Expect.isTrue(set1.contains(set1.elementAt(0)));
-  Expect.isTrue(set1.contains(set1.elementAt(1)));
-  Expect.isTrue(set1.contains(set1.elementAt(2)));
-  Expect.throws(() => set1.elementAt(-1), (e) => e is ArgumentError);
-  Expect.throws(() => set1.elementAt(3), (e) => e is RangeError);
-
-  Expect.throws(
-      () => set2.elementAt("2"), (e) => e is ArgumentError || e is TypeError);
-  Expect.throws(() => set2.elementAt(-1), (e) => e is ArgumentError);
-  Expect.throws(() => set2.elementAt(0), (e) => e is RangeError);
-  Expect.throws(() => set2.elementAt(1), (e) => e is RangeError);
-}