Don't load assets unnecessarily when precompiling executables.

sdk/lib/_internal/pub/test/cache/add/already_cached_test.dart

Index: sdk/lib/_internal/pub/test/cache/add/already_cached_test.dart
diff --git a/sdk/lib/_internal/pub/test/cache/add/already_cached_test.dart b/sdk/lib/_internal/pub/test/cache/add/already_cached_test.dart
index ad68f6c7d1a6d65aaad637e3647737b0b8f39074..f6aaa921bf4f2c0acb4a869de79fcd2b3093b002 100644
--- a/sdk/lib/_internal/pub/test/cache/add/already_cached_test.dart
+++ b/sdk/lib/_internal/pub/test/cache/add/already_cached_test.dart
@@ -10,9 +10,9 @@ import '../../test_pub.dart';
 main() {
   initConfig();
   integration('does nothing if the package is already cached', () {
-    servePackages([
-      packageMap("foo", "1.2.3")
-    ]);
+    servePackages((builder) {
+      builder.serve("foo", "1.2.3");
+    });
 
     // Run once to put it in the cache.
     schedulePub(args: ["cache", "add", "foo"],