Fix analyzer tests in checked mode.

utils/kernel-service/kernel-service.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.
 
 /// This is an interface to the Dart Kernel parser and Kernel binary generator.
 ///
 /// It is used by the kernel-isolate to load Dart source code and generate
 /// Kernel binary format.
 ///
 /// This is either invoked as the root script of the Kernel isolate when used
 /// as a part of
 ///
 ///         dart --dfe=utils/kernel-service/kernel-service.dart ...
 ///
 /// invocation or it is invoked as a standalone script to perform training for
 /// the app-jit snapshot
 ///
 ///         dart utils/kernel-service/kernel-service.dart --train <source-file>
 ///
 ///
 library runtime.tools.kernel_service;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
+import 'package:front_end/file_system.dart';
 import 'package:front_end/memory_file_system.dart';
 import 'package:front_end/physical_file_system.dart';
 import 'package:front_end/src/fasta/vm.dart'
     show CompilationResult, Status, parseScriptInFileSystem;
 
 const bool verbose = const bool.fromEnvironment('DFE_VERBOSE');
 
 const bool strongMode = const bool.fromEnvironment('DFE_STRONG_MODE');
 
 Future<CompilationResult> _processLoadRequestImpl(
@@ skipping 56 matching lines @@
       tag = -tag;
     }
     port.send([tag, inputFileUrl, inputFileUrl, null, result.payload]);
   }
 }
 
 // Given namedSources list of interleaved file name string and
 // raw file content Uint8List this function builds up and returns
 // MemoryFileSystem instance that can be used instead of
 // PhysicalFileSystem.instance by the frontend.
-FileSystem _buildMemoryFileSystem(List namedSources) {
-  FileSystem fileSystem = new MemoryFileSystem(Uri.parse('file:///'));
+MemoryFileSystem _buildMemoryFileSystem(List namedSources) {
+  MemoryFileSystem fileSystem = new MemoryFileSystem(Uri.parse('file:///'));
   for (int i = 0; i < namedSources.length ~/ 2; i++) {
     fileSystem
         .entityForUri(Uri.parse(namedSources[i * 2]))
         .writeAsBytesSync(namedSources[i * 2 + 1]);
   }
   return fileSystem;
 }
 
 train(String scriptUri) {
   // TODO(28532): Enable on Windows.
@@ skipping 19 matching lines @@
 main([args]) {
   if (args?.length == 2 && args[0] == '--train') {
     // This entry point is used when creating an app snapshot. The argument
     // provides a script to compile to warm-up generated code.
     train(args[1]);
   } else {
     // Entry point for the Kernel isolate.
     return new RawReceivePort()..handler = _processLoadRequest;
   }
 }