asap uses timer, not MutationObserver, in Safari

[miedmondson]

asap does not use makeRequestCallFromMutationObserver because if (typeof BrowserMutationObserver === "function") fails: typeof MutationObserver returns "object" in Safari (observed in versions 7-9).

Object.prototype.toString.call(MutationObserver) returns "[object MutationObserverConstructor]".

[rkatic]

Knowing that host/native constructors have sometimes typeof equal to "object", in P the check of existence of a constructor consists in typeof x === "function || typeof y === "object".
I suggest to do similarly here.