Store the async-await compiled pub code directly in the repo.

sdk/lib/_internal/pub_generated/test/barback/fails_if_dir_arg_does_not_exist_test.dart

+import 'package:scheduled_test/scheduled_test.dart';
+import '../../lib/src/exit_codes.dart' as exit_codes;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+main() {
+  initConfig();
+  setUp(() {
+    d.dir(
+        appPath,
+        [d.appPubspec(), d.dir("bar", [d.file("file.txt", "contents")])]).create();
+  });
+  pubBuildAndServeShouldFail(
+      "if a specified directory doesn't exist",
+      args: ["foo", "bar", "baz"],
+      error: 'Directories "foo" and "baz" do not exist.',
+      exitCode: exit_codes.DATA);
+}