fix analysis errors; add missing icon

examples/material_gallery/flutter.yaml

 name: material_gallery
 material-design-icons:
+  - name: navigation/arrow_drop_down
   - name: navigation/cancel
   - name: navigation/menu

examples/material_gallery/lib/main.dart

@@ -6,10 +6,10 @@ import 'package:flutter/material.dart';
 
 import 'chip_demo.dart';
 import 'date_picker_demo.dart';
+import 'drop_down_demo.dart';
 import 'gallery_page.dart';
 import 'time_picker_demo.dart';
 import 'widget_demo.dart';
-import 'drop_down_demo.dart';
 
 final List<WidgetDemo> _kDemos = <WidgetDemo>[
   kChipDemo,

packages/flutter_tools/test/all.dart

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import 'android_device_test.dart' as android_device_test;
-import 'daemon_test.dart' as daemon_test;
-import 'init_test.dart' as init_test;
-import 'install_test.dart' as install_test;
-import 'listen_test.dart' as listen_test;
-import 'list_test.dart' as list_test;
-import 'logs_test.dart' as logs_test;
-import 'os_utils_test.dart' as os_utils_test;
-import 'start_test.dart' as start_test;
-import 'stop_test.dart' as stop_test;
-import 'trace_test.dart' as trace_test;
-
-main() {
-  android_device_test.defineTests();
-  daemon_test.defineTests();
-  init_test.defineTests();
-  install_test.defineTests();
-  listen_test.defineTests();
-  list_test.defineTests();
-  logs_test.defineTests();
-  os_utils_test.defineTests();
-  start_test.defineTests();
-  stop_test.defineTests();
-  trace_test.defineTests();
-}