anchor.diff:    /// Used to store unique keys for library names. Keys are not used as names,
     /// nor are they visible in the output. The only serve as an internal
     /// key into maps.
  -  final Map<LibraryEntity, String> _libraryKeys = HashMap();
  +  final Map<LibraryEntity, String> _libraryKeys = {};
   
     Namer(this._closedWorld, this.fixedNames) {
       _literalGetterPrefix = new StringBackedName(fixedNames.getterPrefix);
  
positive.code: // BSD-style license that can be found in the LICENSE file.
  
  library js_backend.namer;
  
  import 'dart:collection' show HashMap;
  
  import 'package:front_end/src/api_unstable/dart2js.dart'
      show $0, $9, $A, $Z, $_, $a, $g, $s, $z;
  
negative.code:   /// [_disambiguateMember], [_disambiguateInternalMember],
    /// [_disambiguateOperator], and [reservePublicMemberName].
    final NamingScope instanceScope = NamingScope();
    final Map<String, jsAst.Name> userInstanceMembers = {};
    final Map<String, String> userInstanceMembersOriginalName = {};
    final Map<MemberEntity, jsAst.Name> internalInstanceMembers = {};
    final Map<String, jsAst.Name> userInstanceOperators = {};
    final Map<jsAst.Name, jsAst.Name> userGetters = {};
    final Map<jsAst.Name, jsAst.Name> userSetters = {};
    final Map<TypeVariableEntity, jsAst.Name> _typeVariableNames = {};
  
    Map<String, String> createMinifiedInstanceNameMap() {
  