Fix all strong-mode errors and warnings.

test/html_test.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.
 
 @TestOn('browser')
 @Skip(
     "This suite requires a WebSocket server, which is currently unsupported\n"
     "by the test package (dart-lang/test#330). It's currently set up to talk\n"
     "to a hard-coded server on localhost:1234 that is spawned in \n"
     "html_test_server.dart.")
 
 import 'dart:async';
 import 'dart:html';
 import 'dart:typed_data';
 
 import 'package:async/async.dart';
 import 'package:test/test.dart';
 
 import 'package:web_socket_channel/html.dart';
+import 'package:web_socket_channel/web_socket_channel.dart';
 
 void main() {
   var channel;
   tearDown(() {
     if (channel != null) channel.sink.close();
   });
 
   test("communicates using an existing WebSocket", () async {
     var webSocket = new WebSocket("ws://localhost:1234");
     channel = new HtmlWebSocketChannel(webSocket);
@@ skipping 51 matching lines @@
     var channel = new HtmlWebSocketChannel.connect("ws://localhost:1235");
     expect(channel.stream.toList(),
         throwsA(new isInstanceOf<WebSocketChannelException>()));
   });
 }
 
 Future<List<int>> _decodeBlob(Blob blob) async {
   var reader = new FileReader();
   reader.readAsArrayBuffer(blob);
   await reader.onLoad.first;
-  return reader.result;
+  return reader.result as Uint8List;
 }