Create separate scopes for constructors, setters, and other members.

pkg/front_end/lib/src/fasta/builder/mixed_accessor.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.
-
-library fasta.mixed_accessor;
-
-import 'builder.dart' show Builder, LibraryBuilder;
-
-/// Represents the import of a getter and setter from two different libraries.
-class MixedAccessor extends Builder {
-  final Builder getter;
-  final Builder setter;
-
-  MixedAccessor(this.getter, this.setter, LibraryBuilder parent)
-      : super(
-            parent,
-            -1, // Synthetic element has no charOffset.
-            parent.fileUri) {
-    next = getter;
-  }
-
-  @override
-  String get fullNameForErrors => getter.fullNameForErrors;
-}