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

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

+library pub_tests;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+main() {
+  initConfig();
+  integration("watches modifications to files", () {
+    d.dir(
+        appPath,
+        [d.appPubspec(), d.dir("web", [d.file("index.html", "before")])]).create();
+    pubServe();
+    requestShouldSucceed("index.html", "before");
+    d.dir(appPath, [d.dir("web", [d.file("index.html", "after")])]).create();
+    waitForBuildSuccess();
+    requestShouldSucceed("index.html", "after");
+    endPubServe();
+  });
+}