Add "contains" method to Collection.

tests/corelib/collection_contains_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.
+
+// Tests for the contains methods on lists.
+
+test(list, notInList) {
+  testList(list) {
+    for (int i = 0; i < list.length; i++) {
+      var elem = list[i];
+      Expect.isTrue(list.contains(list[i]), "$list.contains($elem)");
+    }
+    Expect.isFalse(list.contains(notInList), "!$list.contains($notInList)");
+  }
+  List fixedList = new List(list.length);
+  List growList = new List();
+  for (int i = 0; i < list.length; i++) {
+    fixedList[i] = list[i];
+    growList.add(list[i]);
+  }
+  testList(list);
+  testList(fixedList);
+  testList(growList);
+}
+
+class C {
+  const C();
+}
+
+class Niet {
+  bool operator==(other) => false;
+}
+
+main() {
+  test(const <String>["a", "b", "c", null], "d");
+  test(const <int>[1, 2, 3, null], 0);
+  test(const <bool>[true, false], null);
+  test(const <C>[const C(), const C(), null], new C());
+  test(<C>[new C(), new C(), new C(), null], new C());
+  test(const <double>[ 0.0, 1.0, 5e-324, 1e+308, double.INFINITY ], 2.0);
+  Expect.isTrue(const <double>[-0.0].contains(0.0));
+  Expect.isFalse(const <double>[double.NAN].contains(double.NAN));
+  var niet = new Niet();
+  Expect.isFalse([niet].contains(niet));
+}