support resolving .packages in FE

pkg/front_end/test/fasta/uri_translator_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 'package:front_end/src/fasta/uri_translator_impl.dart';
+import 'package:package_config/packages.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UriTranslatorImplTest);
   });
 }
 
 @reflectiveTest
 class UriTranslatorImplTest {
   void test_isPlatformImplementation() {
     var translator = new UriTranslatorImpl({
       'core': Uri.parse('file:///sdk/core/core.dart'),
       'math': Uri.parse('file:///sdk/math/math.dart')
-    }, {}, {});
+    }, {}, Packages.noPackages);
 
     bool isPlatform(String uriStr) {
       var uri = Uri.parse(uriStr);
       return translator.isPlatformImplementation(uri);
     }
 
     expect(isPlatform('dart:core/string.dart'), isTrue);
     expect(isPlatform('dart:core'), isFalse);
     expect(isPlatform('dart:_builtin'), isTrue);
     expect(isPlatform('file:///sdk/math/math.dart'), isFalse);
   }
 
   void test_translate_dart() {
     var translator = new UriTranslatorImpl({
       'core': Uri.parse('file:///sdk/core/core.dart'),
       'math': Uri.parse('file:///sdk/math/math.dart')
-    }, {}, {});
+    }, {}, Packages.noPackages);
 
     expect(translator.translate(Uri.parse('dart:core')),
         Uri.parse('file:///sdk/core/core.dart'));
     expect(translator.translate(Uri.parse('dart:core/string.dart')),
         Uri.parse('file:///sdk/core/string.dart'));
 
     expect(translator.translate(Uri.parse('dart:math')),
         Uri.parse('file:///sdk/math/math.dart'));
   }
 }