support resolving .packages in FE

pkg/front_end/test/src/incremental/file_state_test.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 
 import 'package:front_end/memory_file_system.dart';
 import 'package:front_end/src/fasta/uri_translator_impl.dart';
 import 'package:front_end/src/incremental/byte_store.dart';
 import 'package:front_end/src/incremental/file_state.dart';
+import 'package:package_config/packages.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'mock_sdk.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(FileSystemStateTest);
   });
 }
 
 @reflectiveTest
 class FileSystemStateTest {
   final byteStore = new MemoryByteStore();
   final fileSystem = new MemoryFileSystem(Uri.parse('file:///'));
-  final UriTranslatorImpl uriTranslator = new UriTranslatorImpl({}, {}, {});
+  final UriTranslatorImpl uriTranslator =
+      new UriTranslatorImpl({}, {}, Packages.noPackages);
   FileSystemState fsState;
 
   Uri _coreUri;
   List<Uri> _newFileUris = <Uri>[];
 
   void setUp() {
     Map<String, Uri> dartLibraries = createSdkFiles(fileSystem);
     uriTranslator.dartLibraries.addAll(dartLibraries);
     _coreUri = Uri.parse('dart:core');
     expect(_coreUri, isNotNull);
@@ skipping 472 matching lines @@
   }
 
   Uri _writeFileDirectives(String path,
       {List<String> imports: const [], List<String> exports: const []}) {
     return writeFile(path, '''
 ${imports.map((uri) => 'import "$uri";').join('\n')}
 ${exports.map((uri) => 'export "$uri";').join('\n')}
 ''');
   }
 }