
PASS IntersectionObserver in a single document with explicit root. 
PASS First rAF 
PASS document.scrollingElement.scrollTop = window.innerHeight. 
PASS root.scrollTop = 150 with root scrolled into view. 
PASS document.scrollingElement.scrollTop = 0. 
PASS root.scrollTop = 0 
PASS root.scrollTop = 150 with root scrolled out of view.