UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3662.0 Safari/537.36

Steps to reproduce the problem:
1. Make sure you are using windows with a touch screen
2. Open a website (e.g. https://www.youtube.com/)
3. Scroll down and up with your finger by touching the viewport directly
4. Scroll down by dragging the scroll bar on the right

What is the expected behavior?
It should be smooth without any noticeable framerate drops.

What went wrong?
It is a bit laggy with noticeable framerate drops, especially when the edge of the viewport hits a video content. It should be as smooth as scrolling the page directly with a finger.

Did this work before? No 

Chrome version: 73.0.3662.0  Channel: canary
OS Version: 10.0
Flash Version: