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

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

Index: sdk/lib/_internal/pub_generated/test/dart2js/does_not_support_invalid_option_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/dart2js/does_not_support_invalid_option_test.dart b/sdk/lib/_internal/pub_generated/test/dart2js/does_not_support_invalid_option_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6ad75eb31bb0ce0939d22d8d513b6a5e500c1f06
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/test/dart2js/does_not_support_invalid_option_test.dart
@@ -0,0 +1,20 @@
+import '../../lib/src/exit_codes.dart' as exit_codes;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
+main() {
+  initConfig();
+  integration("doesn't support an invalid dart2js option", () {
+    d.dir(appPath, [d.pubspec({
+        "name": "myapp",
+        "transformers": [{
+            "\$dart2js": {
+              "invalidOption": true
+            }
+          }]
+      })]).create();
+    var pub = startPubServe();
+    pub.stderr.expect('Unrecognized dart2js option "invalidOption".');
+    pub.shouldExit(exit_codes.DATA);
+  });
+}