NetworkProcess destructor executes cache storage parameters callbacks since r232863 "Make NetworkProcess get cache storage parameters at creation of the CacheStorage engine", but it's a NeverDestroyed singleton so the destructor is a trap and won't actually run. So the callbacks are not guaranteed to be executed. Youenn, how bad is this? :)
This code is more for completeness. This might prove useful should NetworkProcess does no longer be a singleton. I believe the current behavior to be ok: the callbacks should in theory be triggered when the IPC connection between UIProcess and NetworkProcess is closed. Since this will trigger the end of the NetworkProcess, this is ok to not execute them. It would be a nice refactoring to use an Async reply, this would remove the need for that specific handling.
If the current behavior is OK, no need to keep a bug open for it.