Add support for the metadata we currently support in comments

pkg/meta/meta.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.
+
+/**
+ * This library contains the definitions of annotations that provide additional
+ * semantic information about the program being annotated. These annotations are
+ * intended to be used by tools to provide a better user experience.
+ */
+library meta;
+
+/**
+ * An annotation used to mark a class, field, getter, setter, method, top-level
+ * variable, or top-level function as one that should no longer be used. Tools
+ * can use this annotation to provide a warning on references to the marked
+ * element.
+ */
+const deprecated = const _Deprecated();
+
+class _Deprecated {
+  const _Deprecated();
+}
+
+/**
+ * An annotation used to mark an instance member (method, field, getter or
+ * setter) as one that is intended to be overriding an inherited class member.

[Bob Nystrom, 2012/08/22 20:41:57]

"one that is intended to be overriding" -> "overriding"

[Brian Wilkerson, 2012/08/23 14:52:52]

Done.

+ * Tools can use this annotation to provide a warning if there is no overridden
+ * member.
+ */
+const override = const _Override();
+
+class _Override {
+  const _Override();
+}