Revert "Switch libraries to using new tags."

sdk/lib/collection/maps.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.
 
-part of dart.collection;
-
 /*
  * Helper class which implements complex [Map] operations
  * in term of basic ones ([Map.keys], [Map.operator []],
  * [Map.operator []=] and [Map.remove].)  Not all methods are
  * necessary to implement each particular operation.
  */
 class Maps {
   static bool containsValue(Map map, value) {
     for (final v in map.values) {
       if (value == v) {
@@ skipping 89 matching lines @@
       first = false;
       Collections._emitObject(k, result, visiting);
       result.add(': ');
       Collections._emitObject(v, result, visiting);
     });
 
     result.add('}');
     visiting.removeLast();
   }
 }