UserAgent: Mozilla/5.0 (X11; CrOS x86_64 9928.0.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3212.0 Safari/537.36
Platform: 9928.0.0 (Official Build) canary-channel eve

Steps to reproduce the problem:
1. Have a black scheme, use gMail (black scheme)
2. Open an eMail and scroll around and type something
3. You'll see frequently odd black flashes (single frame, disappear with next frame - have seen triangles as well as rectangles spanning the screen left to right.

What is the expected behavior?
No flashes

What went wrong?
Flashes

Did this work before? Yes Don't know when it started.

Chrome version: 63.0.3212.0  Channel: n/a
OS Version: 9928.0.0
Flash Version: 

Reveman@ - please ping me when you see this!