Extend @protected to include implemented interfaces.

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.
 ///
 /// 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
@@ skipping 51 matching lines @@
 /// Used to annotate a class declaration `C`. Indicates that any type arguments
 /// declared on `C` are to be treated as optional.  Tools such as the analyzer
 /// and linter can use this information to suppress warnings that would
 /// otherwise require type arguments to be provided for instances of `C`.
 const _OptionalTypeArgs optionalTypeArgs = const _OptionalTypeArgs();
 
 /// Used to annotate an instance member (method, getter, setter, operator, or
 /// field) `m` in a class `C`. If the annotation is on a field it applies to the
 /// getter, and setter if appropriate, that are induced by the field. 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.
+/// extend, implement 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
 ///
 /// * the annotation is associated with anything other than an instance member,
 ///   or
 /// * an invocation of a member that has this annotation is used outside of an
 ///   instance member defined on a class that extends or mixes in the class in
 ///   which the protected member is defined, or that uses a receiver other than
 ///   `this`.
 const _Protected protected = const _Protected();
@@ skipping 44 matching lines @@
   const _MustCallSuper();
 }
 
 class _OptionalTypeArgs {
   const _OptionalTypeArgs();
 }
 
 class _Protected {
   const _Protected();
 }