Fix mocked operator methods

tests/lib_strong/html/html_mock_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 'dart:async';
 import 'dart:html';
 
 import 'package:expect/minitest.dart';
 
 class Mock {
-  noSuchMethod(Invocation i) => document;
+  noSuchMethod(Invocation i) {
+    if (this is Window) return document;
+    if (this is FileList) return new MockFile();
+    return null;
+  }
 }
 
 @proxy
 class MockBodyElement extends Mock implements BodyElement {
   Node append(Node e) => e;
 }
 
 class _EventListeners {
   Stream<Event> get onBlur => new Stream.fromIterable([]);
 }
@@ skipping 10 matching lines @@
   Stream<Event> get onBeforeUnload => new Stream.fromIterable([]);
 
   String name = "MOCK_NAME";
 }
 
 @proxy
 class MockLocation extends Mock implements Location {
   String href = "MOCK_HREF";
 }
 
+@proxy
+class MockFileList extends Mock implements FileList {}
+
+@proxy
+class MockFile extends Mock implements File {}
+
 main() {
   test('is', () {
     var win = new MockWindow();
     expect(win is Window, isTrue);
   });
 
   test('getter', () {
     var win = new MockWindow();
     expect(win.document, equals(document));
   });
@@ skipping 19 matching lines @@
     HtmlDocument doc = new MockHtmlDocument();
     expect(doc.body.append(null), equals(null));
   });
 
   test('mixin', () {
     Window win = new MockWindow();
     expect(win.onBlur is Stream, isTrue, reason: 'onBlur should be a stream');
     HtmlDocument doc = new MockHtmlDocument();
     expect(doc.onBlur is Stream, isTrue, reason: 'onBlur should be a stream');
   });
+
+  test('operator', () {
+    var fileList = new MockFileList();
+    expect(fileList[1] is File, isTrue);
+  });
 }