Use FileSystem to read files in SourceLoader and TranslateUri.

pkg/analyzer/lib/src/fasta/analyzer_loader.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_loader;
 
+import 'package:front_end/physical_file_system.dart';
 import 'package:kernel/ast.dart' show Program;
 
 import 'package:front_end/src/fasta/builder/builder.dart' show LibraryBuilder;
 
 import 'package:front_end/src/fasta/target_implementation.dart'
     show TargetImplementation;
 
 import 'package:front_end/src/fasta/source/source_class_builder.dart'
     show SourceClassBuilder;
 
 import 'package:front_end/src/fasta/source/source_loader.dart'
     show SourceLoader;
 
 import 'package:analyzer/src/fasta/element_store.dart' show ElementStore;
 
 import 'analyzer_diet_listener.dart' show AnalyzerDietListener;
 
 class AnalyzerLoader<L> extends SourceLoader<L> {
   ElementStore elementStore;
 
-  AnalyzerLoader(TargetImplementation target) : super(target);
+  AnalyzerLoader(TargetImplementation target)
+      : super(PhysicalFileSystem.instance, target);
 
   @override
   void computeHierarchy(Program program) {
     elementStore = new ElementStore(coreLibrary, builders);
     ticker.logMs("Built analyzer element model.");
   }
 
   @override
   AnalyzerDietListener createDietListener(LibraryBuilder library) {
     return new AnalyzerDietListener(library, elementStore);
   }
 
   @override
   void checkOverrides(List<SourceClassBuilder> sourceClasses) {
     // Not implemented yet. Requires [hierarchy].
   }
 }