Fix warning and hint int test

pkg/mdns/test/decode_test.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 'package:expect/expect.dart';
 import 'package:mdns/src/packet.dart';
 
 main() {
   testValidPackages();
   testBadPackages();
+  testHexDumpList();
 }
 
 testValidPackages() {
   var result;
   result = decodeMDnsResponse(package1);
   Expect.equals(1, result.length);
   Expect.equals('raspberrypi.local', result[0].name);
   Expect.equals('192.168.1.191', result[0].address.address);
 
   result = decodeMDnsResponse(package2);
   Expect.equals(2, result.length);
   Expect.equals('raspberrypi.local', result[0].name);
   Expect.equals('192.168.1.191', result[0].address.address);
   Expect.equals('raspberrypi.local', result[1].name);
   Expect.equals('169.254.95.83', result[1].address.address);
 
   // This packet has no IPv4 address.
   result = decodeMDnsResponse(package3);
   Expect.equals(0, result.length);
 }
 
 testBadPackages() {
   for (var p in [package1, package2, package3]) {
     for (int i = 0; i < p.length; i++) {
       decodeMDnsResponse(p.sublist(0, i));
     }
   }
 }
 
+testHexDumpList() {
+  // Call hexDumpList to get rid of hint.
+  hexDumpList([]);
+}
+
 // One address.
 var package1 = [
     0x00, 0x00, 0x84, 0x00, 0x00, 0x00, 0x00, 0x01,
     0x00, 0x00, 0x00, 0x00, 0x0b, 0x72, 0x61, 0x73,
     0x70, 0x62, 0x65, 0x72, 0x72, 0x79, 0x70, 0x69,
     0x05, 0x6c, 0x6f, 0x63, 0x61, 0x6c, 0x00, 0x00,
     0x01, 0x80, 0x01, 0x00, 0x00, 0x00, 0x78, 0x00,
     0x04, 0xc0, 0xa8, 0x01, 0xbf];
 
 // Two addresses.
@@ skipping 52 matching lines @@
     s += x;
     if (((i + 1) % 8) == 0) {
       s += ',';
       print(s);
       s = '';
     }
   }
   if (s.length != 0) print(s);
 }