function scrollValueMonitor(cb) {
	  var scrollPosition = getUnboundedScrollPosition(window);
	  cb(scrollPosition);
	}
Traps top-level events by using event bubbling.

@param {string} topLevelType Record from `EventConstants`.
@param {string} handlerBaseName Event name (e.g. "click").
@param {object} element Element on which to attach listener.
@return {?object} An object with a remove function which will forcefully
                 remove the listener.
@internal