The behavior of `ApplicationRef.isStable` changed in 16.1 due to
28c68f709c.
This change added a `share` to the `isStable` observable, which prevents
additional subscribers from getting a value until a new one emits. One
solution to the problem would be `shareReplay(1)`. However, that would
increase the bundle size since we do not use `shareReplay` elsewhere.
Instead, we don't even really need to share the observable.
The `Observable` available in `ApplicationRef.isStable` before the above commit
was the zone stable observable, without a `share`. The new behavior adds
only an additional observable to the stream, `hasPendingTasks` (a `BehaviorSubject`).
The observables in this stream are not expensive to subscribe to. The
only one with side effects is the `isStable` (because it subscribes to
onStable), but that one already has the `share` operator on it.
Omitting the `share` in `ApplicationRef` also means that applications on `zoneless` will not
have to pay the cost of the operator when we make zones optional because
the zone stable observable is the only place we use it.
PR Close#53541
629343f247