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

sdk/lib/_internal/pub_generated/test/dart2js/compiles_generated_file_from_dependency_outside_web_test.dart

+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
+main() {
+  initConfig();
+  withBarbackVersions("any", () {
+    integration(
+        "compiles a Dart file that imports a generated file to JS " "outside web/",
+        () {
+      d.dir(appPath, [d.pubspec({
+          "name": "myapp",
+          "version": "0.0.1",
+          "transformers": ["myapp/transformer"]
+        }),
+            d.dir("lib", [d.file("transformer.dart", dartTransformer("munge"))]),
+            d.dir("test", [d.file("main.dart", """
+import "other.dart";
+void main() => print(TOKEN);
+"""), d.file("other.dart", """
+library other;
+const TOKEN = "before";
+""")])]).create();
+      createLockFile('myapp', pkg: ['barback']);
+      pubServe(args: ["test"]);
+      requestShouldSucceed(
+          "main.dart.js",
+          contains("(before, munge)"),
+          root: "test");
+      endPubServe();
+    });
+  });
+}