google-maps: perf: defer event listener subscription

[Akxe]

Feature Description

Currently every google-maps component will add all of its possible event listeners just in case. It might boost performance not to do so until anything listens to this. I a not sure if it is possible with event emitters.

Use Case

Possible performance benefits while using maps components.

[crisbeto]

This should be the case already. See https://github.com/angular/components/blob/master/src/google-maps/google-map/google-map.ts#L463.

[Akxe]

I missed that line on first read through. But won't it break if event listener is added afterwards? I think having native observable with @Output annotation with replayBuffer, (with ref count) might be better suited no?

PS:
Or even better the replayBuffer, transform the stream into reference counted EventEmmiter

[crisbeto]

It would break if the subscription is added after init, but I think the assumption that was made there was that users would subscribe through Angular event bindings.

[Akxe]

Indeed it seems reasonable, though it should be mentioned in comment then, no?

But maybe someone on Google team knows hot to create cold/warm EventEmmiter, anyone? (Pleas tag someone if you know someone who might know)

[crisbeto]

Handled by #17845.

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