Big merge from experimental to bleeding edge.

tests/corelib/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.
+
+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);
+}