Add Hashable to Date interface.

tests/corelib/date_time2_test.dart

Index: tests/corelib/date_time2_test.dart
diff --git a/tests/corelib/date_time2_test.dart b/tests/corelib/date_time2_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..a65b2734708a88bf50a15b538112d9c8f37ee161
--- /dev/null
+++ b/tests/corelib/date_time2_test.dart
@@ -0,0 +1,15 @@
+// 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.
+
+// Dart test program for Date's Hashable.
+
+main() {
+  var d = new Date.fromString("2000-01-01T00:00:00Z");
+  var d2 = new Date.fromString("2000-01-01T00:00:01Z");
+  // There is no guarantee that the hashcode for these two dates is different,
+  // but in the worst case we will have to fix this test.
+  // The important test here is, that Date implements Hashable.
+  Expect.isFalse(d.hashCode() == d2.hashCode());
+  Expect.isTrue(d is Hashable);
+}