Use FileSystem to read files in SourceLoader and TranslateUri.

pkg/front_end/lib/kernel_generator.dart

 // Copyright (c) 2016, 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.
 
 /// Defines the front-end API for converting source code to Dart Kernel objects.
 library front_end.kernel_generator;
 
 import 'compiler_options.dart';
 import 'dart:async' show Future;
 import 'dart:async';
+import 'package:front_end/physical_file_system.dart';
 import 'src/fasta/dill/dill_target.dart' show DillTarget;
 import 'src/fasta/errors.dart' show InputError;
 import 'src/fasta/kernel/kernel_target.dart' show KernelTarget;
 import 'package:kernel/kernel.dart' show Program;
 import 'src/fasta/ticker.dart' show Ticker;
 import 'src/fasta/translate_uri.dart' show TranslateUri;
 import 'src/simple_error.dart';
 
 /// Generates a kernel representation of the program whose main library is in
 /// the given [source].
@@ skipping 21 matching lines @@
     return null;
   }
 
   if (!await fs.entityForUri(source).exists()) {
     return report("Entry-point file not found: $source");
   }
 
   if (!await validateOptions(options)) return null;
 
   try {
-    TranslateUri uriTranslator =
-        await TranslateUri.parse(null, options.packagesFileUri);
+    TranslateUri uriTranslator = await TranslateUri.parse(
+        PhysicalFileSystem.instance, null, options.packagesFileUri);
 
     var dillTarget =
         new DillTarget(new Ticker(isVerbose: false), uriTranslator);
     var summary = options.sdkSummary;
     if (summary != null) dillTarget.read(summary);
 
-    var kernelTarget =
-        new KernelTarget(dillTarget, uriTranslator, options.strongMode);
+    var kernelTarget = new KernelTarget(
+        options.fileSystem, dillTarget, uriTranslator, options.strongMode);
     kernelTarget.read(source);
 
     await dillTarget.writeOutline(null);
     await kernelTarget.writeOutline(null);
     Program program = await kernelTarget.writeProgram(null);
 
     if (kernelTarget.errors.isNotEmpty) {
       kernelTarget.errors.forEach((e) => report('$e'));
       return null;
     }
@@ skipping 43 matching lines @@
 /// TODO(paulberry): would it be better to define a data type in kernel to
 /// represent a bundle of all the libraries in a given build unit?
 ///
 /// TODO(paulberry): does additional information need to be output to allow the
 /// caller to match up referenced elements to the summary files they were
 /// obtained from?
 Future<Program> kernelForBuildUnit(
     List<Uri> sources, CompilerOptions options) async {
   throw new UnimplementedError("kernel for build-unit is not implemented");
 }