Fix all strong-mode errors and warnings.

lib/src/util/io.dart

 // Copyright (c) 2015, 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:convert';
 import 'dart:io';
 import 'dart:mirrors';
 
 import 'package:path/path.dart' as p;
@@ skipping 145 matching lines @@
 
 /// Repeatedly finds a probably-unused port on localhost and passes it to
 /// [tryPort] until it binds successfully.
 ///
 /// [tryPort] should return a non-`null` value or a Future completing to a
 /// non-`null` value once it binds successfully. This value will be returned
 /// by [getUnusedPort] in turn.
 ///
 /// This is necessary for ensuring that our port binding isn't flaky for
 /// applications that don't print out the bound port.
-Future getUnusedPort(tryPort(int port)) {
-  var value;
+Future/*<T>*/ getUnusedPort/*<T>*/(/*=T*/ tryPort(int port)) {
+  var/*=T*/ value;
   return Future.doWhile(() async {
     value = await tryPort(await getUnsafeUnusedPort());
     return value == null;
   }).then((_) => value);
 }
 
 /// Returns a port that is probably, but not definitely, not in use.
 ///
 /// This has a built-in race condition: another process may bind this port at
 /// any time after this call has returned. If at all possible, callers should
 /// use [getUnusedPort] instead.
 Future<int> getUnsafeUnusedPort() async {
   var socket = await RawServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0);
   var port = socket.port;
   await socket.close();
   return port;
 }