Implement Date.

dart/frog/leg/lib/date_helper.dart

Index: dart/frog/leg/lib/date_helper.dart
diff --git a/dart/frog/leg/lib/date_helper.dart b/dart/frog/leg/lib/date_helper.dart
new file mode 100644
index 0000000000000000000000000000000000000000..9c19ac66ac2a579df578a3155b076de40a243f11
--- /dev/null
+++ b/dart/frog/leg/lib/date_helper.dart
@@ -0,0 +1,14 @@
+// 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.
+
+String threeDigits(int n) {
+  if (n >= 100) return "${n}";
+  if (n > 10) return "0${n}";
+  return "00${n}";
+}
+
+String twoDigits(int n) {
+  if (n >= 10) return "${n}";
+  return "0${n}";
+}