Don't load assets unnecessarily when precompiling executables.

sdk/lib/_internal/pub/test/global/run/runs_script_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.
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   initConfig();
   integration('runs a script in an activated package', () {
-    servePackages([
-      packageMap("foo", "1.0.0")
-    ], contents: [
-      d.dir("bin", [
-        d.file("script.dart", "main(args) => print('ok');")
-      ])
-    ]);
+    servePackages((builder) {
+      builder.serve("foo", "1.0.0", contents: [
+        d.dir("bin", [
+          d.file("script.dart", "main(args) => print('ok');")
+        ])
+      ]);
+    });
 
     schedulePub(args: ["global", "activate", "foo"]);
 
     var pub = pubRun(global: true, args: ["foo:script"]);
     pub.stdout.expect("ok");
     pub.shouldExit();
   });
 }