Steps to reproduce the problem:
1. Add an element to the page that uses viewport height units
2. Scroll the page up and down causing the new bottom toolbar to show/hide

What is the expected behavior?
The viewport height units do not change value.

What went wrong?
The viewport height units change value as the bottom bar is show/hidden.

Did this work before? Yes 

Chrome version: 69.0.3497.105  Channel: stable
OS Version: 12.0
Flash Version: 

You can use this demo to see the issue: https://s.codepen.io/graygilmore/debug/522b8d8eb61955dc9ac4c9c7175d8664

Note that this regression is not present on iOS Safari which I believe is the goal for vh functionality.