Make servePackages's contents argument saner.

sdk/lib/_internal/pub/test/cache/repair/handles_failure_test.dart

 // Copyright (c) 2014, 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 'package:scheduled_test/scheduled_test.dart';
 
 import '../../../lib/src/exit_codes.dart' as exit_codes;
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   integration('handles failure to reinstall some packages', () {
     // Only serve two packages so repairing will have a failure.
-    servePackages([
-      packageMap("foo", "1.2.3"),
-      packageMap("foo", "1.2.5")
-    ]);
+    servePackages((builder) {
+      builder.serve("foo", "1.2.3");
+      builder.serve("foo", "1.2.5");
+    });
 
     // Set up a cache with some packages.
     d.dir(cachePath, [
       d.dir('hosted', [
         d.async(port.then((p) => d.dir('localhost%58$p', [
           d.dir("foo-1.2.3", [
             d.libPubspec("foo", "1.2.3"),
             d.file("broken.txt")
           ]),
           d.dir("foo-1.2.4", [
@@ skipping 17 matching lines @@
 
     pub.stderr.expect(startsWith("Failed to repair foo 1.2.4. Error:"));
     pub.stderr.expect("HTTP error 404: Not Found");
 
     pub.stdout.expect("Reinstalled 2 packages.");
     pub.stdout.expect("Failed to reinstall 1 package.");
 
     pub.shouldExit(exit_codes.UNAVAILABLE);
   });
 }