Start actually adding incrementality into incremental kernel generator.

pkg/front_end/test/src/incremental/file_state_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/memory_file_system.dart';
 import 'package:front_end/src/fasta/translate_uri.dart';
 import 'package:front_end/src/incremental/file_state.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'mock_sdk.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(FileSystemStateTest);
   });
 }
 
 @reflectiveTest
 class FileSystemStateTest {
   final fileSystem = new MemoryFileSystem(Uri.parse('file:///'));
   final TranslateUri uriTranslator = new TranslateUri({}, {});
   FileSystemState fsState;
 
   Uri _coreUri;
 
   void setUp() {
     Map<String, Uri> dartLibraries = createSdkFiles(fileSystem);
     uriTranslator.dartLibraries.addAll(dartLibraries);
-    _coreUri = uriTranslator.dartLibraries['core'];
+    _coreUri = Uri.parse('dart:core');
     expect(_coreUri, isNotNull);
     fsState = new FileSystemState(fileSystem, uriTranslator);
   }
 
   test_getFile() async {
     var a = writeFile('/a.dart', '');
     var b = writeFile('/b.dart', '');
     var c = writeFile('/c.dart', '');
     var d = writeFile(
         '/d.dart',
@@ skipping 87 matching lines @@
 
   /// Write the given [text] of the file with the given [path] into the
   /// virtual filesystem.  Return the URI of the file.
   Uri writeFile(String path, String text) {
     Uri uri = Uri.parse('file://$path');
     fileSystem.entityForUri(uri).writeAsStringSync(text);
     return uri;
   }
 
   void _assertImportedUris(FileState file, List<Uri> expectedUris) {
-    Iterable<Uri> importedUris = _toFileUris(file.importedLibraries);
+    Iterable<Uri> importedUris = _toUris(file.importedLibraries);
     expect(importedUris, unorderedEquals(expectedUris));
   }
 
-  Iterable<Uri> _toFileUris(List<FileState> files) {
-    return files.map((f) => f.fileUri);
+  Iterable<Uri> _toUris(List<FileState> files) {
+    return files.map((f) => f.uri);
   }
 
   Uri _writeFileDirectives(String path,
       {List<String> imports: const [], List<String> exports: const []}) {
     return writeFile(
         path,
         '''
 ${imports.map((uri) => 'import "$uri";').join('\n')}
 ${exports.map((uri) => 'export "$uri";').join('\n')}
 ''');
   }
 }