Set empty namespaces for public/exportNamespace of synthetic libraries.

pkg/analyzer/lib/src/dart/resolver/scope.dart

 // Copyright (c) 2014, 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 analyzer.src.dart.resolver.scope;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 645 matching lines @@
 class Namespace {
   /**
    * An empty namespace.
    */
   static Namespace EMPTY = new Namespace(new HashMap<String, Element>());
 
   /**
    * A table mapping names that are defined in this namespace to the element
    * representing the thing declared with that name.
    */
-  final HashMap<String, Element> _definedNames;
+  final Map<String, Element> _definedNames;
 
   /**
    * Initialize a newly created namespace to have the [_definedNames].
    */
   Namespace(this._definedNames);
 
   /**
    * Return a table containing the same mappings as those defined by this
    * namespace.
    */
@@ skipping 489 matching lines @@
 
   /**
    * Define the type parameters declared by the [classElement].
    */
   void _defineTypeParameters(ClassElement classElement) {
     for (TypeParameterElement typeParameter in classElement.typeParameters) {
       define(typeParameter);
     }
   }
 }