Make servePackages's contents argument saner.

sdk/lib/_internal/pub/test/get/hosted/get_test.dart

 // Copyright (c) 2012, 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.
 
 library pub_tests;
 
 import '../../../lib/src/exit_codes.dart' as exit_codes;
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   integration('gets a package from a pub server', () {
-    servePackages([packageMap("foo", "1.2.3")]);
+    servePackages((builder) => builder.serve("foo", "1.2.3"));
 
     d.appDir({"foo": "1.2.3"}).create();
 
     pubGet();
 
     d.cacheDir({"foo": "1.2.3"}).validate();
     d.packagesDir({"foo": "1.2.3"}).validate();
   });
 
   integration('URL encodes the package name', () {
-    servePackages([]);
+    serveNoPackages();
 
     d.appDir({"bad name!": "1.2.3"}).create();
 
     pubGet(
         error: new RegExp(
           r"Could not find package bad name! at http://localhost:\d+\."),
         exitCode: exit_codes.UNAVAILABLE);
   });
 }