Add ordered set.

tests/corelib/ordered_set_iterator_test.dart

+// Copyright (c) 2011, 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() {
+  var it, i;
+  var entries = [1, 2, 3, 4, 499, 42];
+  var set = new OrderedSet();
+  set.addAll(entries);
+
+  Expect.listEquals([1, 2, 3, 4, 499, 42], set.toList());
+  it = set.iterator;
+  i = 0;
+  while (it.moveNext()) {
+    Expect.equals(entries[i++], it.current);
+  }
+  // Add the entries in reverse order and make sure that this doesn't change
+  // the internal order.
+  for (int j = entries.length - 1; j >= 0; j--) {
+    set.add(entries[j]);
+  }
+  Expect.listEquals([1, 2, 3, 4, 499, 42], set.toList());
+  it = set.iterator;
+  i = 0;
+  while (it.moveNext()) {
+    Expect.equals(entries[i++], it.current);
+  }
+
+  set = new OrderedSet.from(entries);
+  Expect.listEquals([1, 2, 3, 4, 499, 42], set.toList());
+  it = set.iterator;
+  i = 0;
+  while (it.moveNext()) {
+    Expect.equals(entries[i++], it.current);
+  }
+  // Add the entries in reverse order and make sure that this doesn't change
+  // the internal order.
+  for (int j = entries.length - 1; j >= 0; j--) {
+    set.add(entries[j]);
+  }
+  Expect.listEquals([1, 2, 3, 4, 499, 42], set.toList());
+  it = set.iterator;
+  i = 0;
+  while (it.moveNext()) {
+    Expect.equals(entries[i++], it.current);
+  }
+}