Add the @protected annotation

pkg/meta/lib/meta.dart

 // Copyright (c) 2016, 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.
 
 /**
  * Constants for use in metadata annotations such as `@protected`.
  *
  * See also `@deprecated` and `@override` in the `dart:core` library.
  *
  * Annotations provide semantic information
  * that tools can use to provide a better user experience.
  * For example, an IDE might not autocomplete
  * the name of a function that's been marked `@deprecated`,
  * or it might display the function's name differently.
  *
  * For information on installing and importing this library, see the
  * [meta package on pub.dartlang.org]
  * (http://pub.dartlang.org/packages/meta).
  * For examples of using annotations, see
  * [Metadata](https://www.dartlang.org/docs/dart-up-and-running/ch02.html#metadata)
  * in the language tour.
  */
 library meta;
+
+/**
+ * Used to annotate an instance method `m` in a class `C`. Indicates that `m`
+ * should only be invoked from instance methods of `C` or classes that extend or
+ * mix in `C`, either directly or indirectly. Additionally indicates that `m`
+ * should only be invoked on `this`, whether explicitly or implicitly.
+ *
+ * Tools, such as the analyzer, can provide feedback if an invocation of a
+ * method marked as being protected is used outside of an instance method
+ * defined on a class that extends or mixes in the class in which the protected
+ * method is defined, or that uses a receiver other than `this`.
+ */

[Bob Nystrom, 2016/02/17 19:35:07]

I understand if analyzer uses /** */ for historical reasons, but this is a
separate package and should really follow the style guide.

Who knows, you may even eventually start liking "///". :)

[pquitslund, 2016/02/17 19:35:51]

Any chance we can jump to the future and adopt `///`-style comments?

[Brian Wilkerson, 2016/02/17 20:53:19]

As much as I prefer "/**" style comments, I was resigned to the need to bow to
the prevailing winds. Then I noticed that the file already used "/**" comments
for the library doc comment, so I went with the flow. Was I wrong to preserve
the already established style?

+const _Protected protected = const _Protected();
+
+class _Protected {
+  const _Protected();
+}