UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.167 Safari/537.36

Steps to reproduce the problem:
1. Set iframe with a scroll height smaller than than iframe height
2. Use js to change the scroll-height to be bigger (i.e set min-height:5000px to body)

What is the expected behavior?
Scrollbar should be added quickly

What went wrong?
The entire iframe is reloaded with a significant lag.

Did this work before? Yes 64.0.3282.167

Does this work in other browsers? Yes

Chrome version: 66.0.3350.0  Channel: canary
OS Version: 10.0
Flash Version: