ThirdPartyCredentialManagerImpl: no tab-visibility gate

Precondition: Chrome on Android, third-party password manager set as system Autofill service, and Chrome → Settings → Autofill Options → "Autofill using another service" enabled.

1. Load this page (attacker tab).
2. Open a new tab (e.g. your bank's login page) so this tab becomes hidden.
3. Watch the Android system Credential Manager bottom sheet repeatedly appear over the foreground tab even though this hidden tab requested it. Dismiss it — it reappears ~2 s later (no PENDING_REQUEST throttle).
4. Variant: navigate this tab to about:blank while a sheet is showing — the sheet survives (null CancellationSignal, empty ResetAfterDisconnecting()).

Arm: fire when tab becomes hidden Fire once now (sanity check) Disarm  |  store() variant →