Make servePackages's contents argument saner.

sdk/lib/_internal/pub/test/get/hosted/resolve_constraints_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 '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   integration('resolves version constraints from a pub server', () {
-    servePackages([
-      packageMap("foo", "1.2.3", {"baz": ">=2.0.0"}),
-      packageMap("bar", "2.3.4", {"baz": "<3.0.0"}),
-      packageMap("baz", "2.0.3"),
-      packageMap("baz", "2.0.4"),
-      packageMap("baz", "3.0.1")
-    ]);
+    servePackages((builder) {
+      builder.serve("foo", "1.2.3", pubspec: {
+        "dependencies": {"baz": ">=2.0.0"}
+      });
+      builder.serve("bar", "2.3.4", pubspec: {
+        "dependencies": {"baz": "<3.0.0"}
+      });
+      builder.serve("baz", "2.0.3");
+      builder.serve("baz", "2.0.4");
+      builder.serve("baz", "3.0.1");
+    });
 
     d.appDir({"foo": "any", "bar": "any"}).create();
 
     pubGet();
 
     d.cacheDir({
       "foo": "1.2.3",
       "bar": "2.3.4",
       "baz": "2.0.4"
     }).validate();
 
     d.packagesDir({
       "foo": "1.2.3",
       "bar": "2.3.4",
       "baz": "2.0.4"
     }).validate();
   });
 }