code: function checkActivePlaceholders() {
  	const placeholdersCount = activePlaceholders.length;
  	debug( `Checking active placeholders. Count: ${ placeholdersCount }` );
  
  	if ( placeholdersCount > 0 ) {
  		activePlaceholderEverDetected = true;
  	}
  
  	// record event if there ever were any placeholders and if they all just disappeared
  	if ( activePlaceholderEverDetected && placeholdersCount === 0 ) {
  		// tell tracks to record duration
  		const { startTime, trigger } = determineTimingType();
  		const duration = Math.round( performance.now() - startTime );
  		debug( `Recording placeholder wait. Duration: ${ duration }, Trigger: ${ trigger }` );
  		analytics.timing.record( `placeholder-wait.${ trigger }`, duration );
  		stopMutationObserver();
  	}
  }
docs: Check if there are any placeholders on the screen and trigger a timing event when all the placeholders are gone