Chrome Version: 63.0.3214.0
OS: Android

What steps will reproduce the problem?
(1) Enable Chrome Home experiment in chrome://flags (so that URL bar is at the bottom)
(2) Visit http://bokand.github.io/vvHeight.html
(3) Scroll down so that the URL bar hides but don't lift your finger.

What is the expected result?
The visualViewport.height value should increase in real-time as the URL bar hides

What happens instead?
The visualViewport.height value doesn't change until the finger is lifted.