Was incorrectly checking for overflow using getBoundingClientRect(), which wasn't consistently returning the width of the child element if there was actually overflow in the parent.
Coverage increased (+0.1%) to 93.913% when pulling 3bb27a20932c458d29d17f77b50ce331ce6c9670 on overflow-fix into 24852b2b77126c52a94fefb33d71aa87a8b31803 on master.
Was incorrectly checking for overflow using getBoundingClientRect(), which wasn't consistently returning the width of the child element if there was actually overflow in the parent.