Chrome Version       : 68.0.3440.4
OS Version: 10718.4.0

What steps will reproduce the problem?
1. Connect Pixelbook to an external 4K monitor
2. Set "Display Size" for that monitor to 200%
3. Plug in an external mouse

What is the expected result?

Mouse speed should feel "normal".

What happens instead of that?

Mouse is waaay to jumpy on the external screen while it feels perfectly decent on the primary display. Even when I set mouse speed to slowest in settings, it's still too fast to use it.  

I suspect we aren't properly tweaking the speed based on settings in #2.

Please provide any additional information below. Attach a screenshot if
possible.

UserAgentString: Mozilla/5.0 (X11; CrOS x86_64 10718.4.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.4 Safari/537.36