Make servePackages's contents argument saner.

sdk/lib/_internal/pub/test/snapshot/upgrades_snapshot_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:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
   integration("upgrades a snapshot when its package is upgraded", () {
-    servePackages([packageMap("foo", "1.2.3")], contents: [
-      d.dir("bin", [
-        d.file("hello.dart", "void main() => print('hello!');")
-      ])
-    ]);
+    servePackages((builder) {
+      builder.serve("foo", "1.2.3", contents: [
+        d.dir("bin", [
+          d.file("hello.dart", "void main() => print('hello!');")
+        ])
+      ]);
+    });
 
     d.appDir({"foo": "any"}).create();
 
     pubGet(output: contains("Precompiled foo:hello."));
 
     d.dir(p.join(appPath, '.pub', 'bin', 'foo'), [
       d.matcherFile('hello.dart.snapshot', contains('hello!'))
     ]).validate();
 
-    servePackages([packageMap("foo", "1.2.4")], contents: [
-      d.dir("bin", [
-        d.file("hello.dart", "void main() => print('hello 2!');")
-      ])
-    ]);
+    servePackages((builder) {
+      builder.serve("foo", "1.2.4", contents: [
+        d.dir("bin", [
+          d.file("hello.dart", "void main() => print('hello 2!');")
+        ])
+      ]);
+    });
 
     pubUpgrade(output: contains("Precompiled foo:hello."));
 
     d.dir(p.join(appPath, '.pub', 'bin', 'foo'), [
       d.matcherFile('hello.dart.snapshot', contains('hello 2!'))
     ]).validate();
 
     var process = pubRun(args: ['foo:hello']);
     process.stdout.expect("hello 2!");
     process.shouldExit();
   });
 }