Make constant lists immutable

pkg/analyzer/test/source/package_map_resolver_test.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 test.source.package_map_resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
@@ skipping 37 matching lines @@
       new _PackageMapUriResolverTest().test_resolve_package_notInMap();
     });
     test('restoreAbsolute_OK', () {
       new _PackageMapUriResolverTest().test_restoreAbsolute();
     });
   });
 }
 
 
 class _PackageMapUriResolverTest {
-  static HashMap EMPTY_MAP = new HashMap<String, List<Folder>>();
+  static const Map EMPTY_MAP = const <String, List<Folder>>{};
   MemoryResourceProvider provider = new MemoryResourceProvider();
 
   void test_isPackageUri() {
     Uri uri = Uri.parse('package:test/test.dart');
     expect(uri.scheme, 'package');
     expect(PackageMapUriResolver.isPackageUri(uri), isTrue);
   }
 
   void test_isPackageUri_null_scheme() {
     Uri uri = Uri.parse('foo.dart');
@@ skipping 127 matching lines @@
       Source source = _createFileSource('/no/such/file');
       Uri uri = resolver.restoreAbsolute(source);
       expect(uri, isNull);
     }
   }
 
   Source _createFileSource(String path) {
     return new NonExistingSource(path, UriKind.FILE_URI);
   }
 }