updateObservers_() {
        // Collect observers that have active observations.
        const activeObservers = this.observers_.filter(observer => {
            return observer.gatherActive(), observer.hasActive();
        });

        // Deliver notifications in a separate cycle in order to avoid any
        // collisions between observers, e.g. when multiple instances of
        // ResizeObserver are tracking the same element and the callback of one
        // of them changes content dimensions of the observed target. Sometimes
        // this may result in notifications being blocked for the rest of observers.
        activeObservers.forEach(observer => observer.broadcastActive());

        return activeObservers.length > 0;
    }
Updates every observer from observers list and notifies them of queued
entries.

@private
@returns {boolean} Returns "true" if any observer has detected changes in
     dimensions of it's elements.