src/vs/base/common/observableImpl/autorun.ts/AutorunObserver/handleChange
class AutorunObserver:	public handleChange<T, TChange>(observable: IObservable<T, TChange>, change: TChange): void {
		const shouldReact = this._handleChange ? this._handleChange({
			changedObservable: observable,
			change,
			didChange: o => o === observable as any,
		}) : true;
		this.needsToRun = this.needsToRun || shouldReact;

		if (this.updateCount === 0) {
			this.runIfNeeded();
		}
	}