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

sdk/lib/_internal/pub_generated/test/transformer/runs_a_third_party_transformer_on_a_local_transformer_test.dart

+library pub_tests;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
+main() {
+  initConfig();
+  withBarbackVersions("any", () {
+    integration("runs a third-party transformer on a local transformer", () {
+      d.dir(
+          "foo",
+          [
+              d.libPubspec("foo", '1.0.0'),
+              d.dir("lib", [d.file("transformer.dart", dartTransformer('foo'))])]).create();
+      d.dir(appPath, [d.pubspec({
+          "name": "myapp",
+          "transformers": ["foo/transformer", "myapp/transformer"],
+          "dependencies": {
+            "foo": {
+              "path": "../foo"
+            }
+          }
+        }),
+            d.dir("lib", [d.file("transformer.dart", dartTransformer('myapp'))]),
+            d.dir("web", [d.file("main.dart", 'const TOKEN = "main.dart";')])]).create();
+      createLockFile('myapp', sandbox: ['foo'], pkg: ['barback']);
+      pubServe();
+      requestShouldSucceed(
+          "main.dart",
+          'const TOKEN = "((main.dart, foo), (myapp, foo))";');
+      endPubServe();
+    });
+  });
+}