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

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

+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
+main() {
+  initConfig();
+  integration("supports most dart2js command-line options", () {
+    d.dir(appPath, [d.pubspec({
+        "name": "myapp",
+        "transformers": [{
+            "\$dart2js": {
+              "commandLineOptions": ["--enable-diagnostic-colors"],
+              "checked": true,
+              "csp": true,
+              "minify": true,
+              "verbose": true,
+              "environment": {
+                "name": "value"
+              },
+              "analyzeAll": true,
+              "suppressWarnings": true,
+              "suppressHints": true,
+              "suppressPackageWarnings": false,
+              "terse": true
+            }
+          }]
+      })]).create();
+    pubServe();
+    requestShouldSucceed("main.dart.js", isNot(isEmpty));
+    endPubServe();
+  });
+}