
issue: https://github.com/flutter/flutter/issues/159745 https://github.com/flutter/engine/pull/56927 introduced untracked handles, but naming them didn't work. This adds a test to make sure they work. I kept naming thread-safe since it isn't happening often anyways. [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style