Use FileSystem to read files in SourceLoader and TranslateUri.

pkg/analyzer/lib/src/fasta/analyzer_target.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.
 
 library fasta.analyzer_target;
 
+import 'package:front_end/physical_file_system.dart';
 import 'package:kernel/ast.dart' show Library, Source;
 
 import 'package:front_end/src/fasta/kernel/kernel_target.dart'
     show KernelTarget;
 
 import 'package:front_end/src/fasta/translate_uri.dart' show TranslateUri;
 
 import 'package:front_end/src/fasta/dill/dill_target.dart' show DillTarget;
 
 import 'analyzer_loader.dart' show AnalyzerLoader;
 
 class AnalyzerTarget extends KernelTarget {
   AnalyzerTarget(
       DillTarget dillTarget, TranslateUri uriTranslator, bool strongMode,
       [Map<String, Source> uriToSource])
-      : super(dillTarget, uriTranslator, strongMode, uriToSource);
+      : super(PhysicalFileSystem.instance, dillTarget, uriTranslator,
+            strongMode, uriToSource);
 
   @override
   AnalyzerLoader<Library> createLoader() => new AnalyzerLoader<Library>(this);
 }