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

sdk/lib/_internal/pub_generated/test/get/dry_run_does_not_apply_changes_test.dart

+import 'package:scheduled_test/scheduled_test.dart';
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+main() {
+  initConfig();
+  integration("--dry-run shows but does not apply changes", () {
+    servePackages((builder) {
+      builder.serve("foo", "1.0.0");
+    });
+    d.appDir({
+      "foo": "1.0.0"
+    }).create();
+    pubGet(
+        args: ["--dry-run"],
+        output: allOf(
+            [contains("+ foo 1.0.0"), contains("Would change 1 dependency.")]));
+    d.dir(
+        appPath,
+        [d.nothing("pubspec.lock"), d.nothing("packages")]).validate();
+  });
+}