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

sdk/lib/_internal/pub_generated/test/serve/does_not_crash_if_an_unused_dart_file_has_a_syntax_error_test.dart

+library pub_tests;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+main() {
+  initConfig();
+  withBarbackVersions("any", () {
+    integration("doesn't crash if an unused .dart file has a syntax error", () {
+      d.dir(appPath, [d.pubspec({
+          "name": "myapp",
+          "transformers": ["myapp/src/transformer"]
+        }),
+            d.dir(
+                "lib",
+                [
+                    d.dir(
+                        "src",
+                        [
+                            d.file("transformer.dart", REWRITE_TRANSFORMER),
+                            d.file("unused.dart", "(*&^#@")])]),
+            d.dir("web", [d.file("foo.txt", "foo")])]).create();
+      createLockFile('myapp', pkg: ['barback']);
+      var server = pubServe();
+      requestShouldSucceed("foo.out", "foo.out");
+      endPubServe();
+    });
+  });
+}