Make servePackages's contents argument saner.

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

Index: sdk/lib/_internal/pub/test/cache/add/no_matching_version_test.dart
diff --git a/sdk/lib/_internal/pub/test/cache/add/no_matching_version_test.dart b/sdk/lib/_internal/pub/test/cache/add/no_matching_version_test.dart
index 2f8cc3531003126e3b898fe48f8d71d8695f0029..53fd3c573d3aa036378068d2036f215975825070 100644
--- a/sdk/lib/_internal/pub/test/cache/add/no_matching_version_test.dart
+++ b/sdk/lib/_internal/pub/test/cache/add/no_matching_version_test.dart
@@ -9,10 +9,10 @@ import '../../test_pub.dart';
 main() {
   initConfig();
   integration('fails if no version matches the version constraint', () {
-    servePackages([
-      packageMap("foo", "1.2.2"),
-      packageMap("foo", "1.2.3")
-    ]);
+    servePackages((builder) {
+      builder.serve("foo", "1.2.2");
+      builder.serve("foo", "1.2.3");
+    });
 
     schedulePub(args: ["cache", "add", "foo", "-v", ">2.0.0"],
         error: 'Package foo has no versions that match >2.0.0.',