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

sdk/lib/_internal/pub_generated/test/cache/repair/empty_cache_test.dart

+library pub_tests;
+import '../../test_pub.dart';
+main() {
+  initConfig();
+  integration('does nothing if the cache is empty', () {
+    schedulePub(
+        args: ["cache", "repair"],
+        output: "No packages in cache, so nothing to repair.");
+  });
+}