Fix mocked operator methods

tests/lib_strong/html/html_mock_test.dart

Index: tests/lib_strong/html/html_mock_test.dart
diff --git a/tests/lib_strong/html/html_mock_test.dart b/tests/lib_strong/html/html_mock_test.dart
index b470495181cb5079587208341a119f84cc34f7d6..1d4aeb9e5e1ee9287dafa82f45ed371caf9515e7 100644
--- a/tests/lib_strong/html/html_mock_test.dart
+++ b/tests/lib_strong/html/html_mock_test.dart
@@ -8,7 +8,11 @@ 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
@@ -39,6 +43,12 @@ 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();
@@ -78,4 +88,9 @@ main() {
     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);
+  });
 }