Diagnose missing @MirrorsUsed.

dart/sdk/lib/mirrors/mirrors.dart

 // Copyright (c) 2013, 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.
 
 // For the purposes of the mirrors library, we adopt a naming
 // convention with respect to getters and setters.  Specifically, for
 // some variable or field...
 //
 //   var myField;
 //
@@ skipping 1086 matching lines @@
    *
    * That is, that the comment is either enclosed in [: /** ... */ :] or starts
    * with [: /// :].
    */
   final bool isDocComment;
 
   const Comment(this.text, this.trimmedText, this.isDocComment);
 }
 
 /**
- * EXPERIMENTAL API: Description of how "dart:mirrors" is used.
+ * Annotation describing how "dart:mirrors" is used (EXPERIMENTAL).
  *
  * When used as metadata on an import of "dart:mirrors" in library *L*, this
  * class describes how "dart:mirrors" is used by library *L* unless overridden.
  * See [override].
  *
  * The following text is non-normative:

[Kathy Walrath, 2013/12/03 17:28:30]

I'd probably just delete this paragraph. Our API docs are aimed at API users,
not reimplementers (unlike the Java docs, which tried to serve both audiences),
so normative vs. non-normative doesn't seem to make sense here.

  *
  * In some scenarios, for example, when minifying Dart code, or when generating
  * JavaScript code from a Dart program, the size and performance of the output
  * can suffer from use of reflection.  In those cases, telling the compiler
  * what is used, can have a significant impact.
  *
  * Example usage:
  *
  *     @MirrorsUsed(symbols: 'foo', override: '*')
  *     import 'dart:mirrors';
  *
  *     class Foo {
  *       noSuchMethod(Invocation invocation) {
- *         print(Mirrors.getName(invocation.memberName));
+ *         print(MirrorSystem.getName(invocation.memberName));
  *       }
  *     }
  *
  *     main() {
  *       new Foo().foo(); // Prints "foo".
  *       new Foo().bar(); // Might print an arbitrary (mangled) name, "bar".
  *     }
  */
 // TODO(ahe): Remove ", override: '*'" when it isn't necessary anymore.
 class MirrorsUsed {
@@ skipping 56 matching lines @@
    *
    * When used as metadata on an import of "dart:mirrors", this metadata does
    * not apply to the library in which the annotation is used, but instead
    * applies to the other libraries (all libraries if "*" is used).
    */
   final override;
 
   const MirrorsUsed(
       {this.symbols, this.targets, this.metaTargets, this.override});
 }