UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.139 Safari/537.36

Steps to reproduce the problem:
Example with the YouTube's `position: fixed` navbar:

Safari: https://gfycat.com/FaithfulVengefulBronco
Chrome: https://gfycat.com/FineDisgustingHarlequinbug

What is the expected behavior?
Fixed elements should not move with the rest of the content due to elastic scroll.

What went wrong?
Fixed elements move.

Did this work before? N/A 

Chrome version: 66.0.3359.139  Channel: stable
OS Version: OS X 10.13.4
Flash Version: 

This would be related to: https://bugs.chromium.org/p/chromium/issues/detail?id=546520

Could these two issues please be prioritized? Scrolling is one of the most important parts of the web experience, and having these two parts nailed would greatly improve the web and Electron apps on macOS.