Chrome Version: 70.0.3538.7 
Chrome OS Version: 11021.5.0
Chrome OS Platform: careena

Steps To Reproduce:
(1) Enable "auto-hide shelf"
(2) mouse down to show shelf then up to hide it several times
(3)

Expected Result:

Shelf is shown cleanly each time

Actual Result:

Sometimes shelf is "squared" (no rounded edges)
Sometimes shelf corner (ie above the rounded edges) has some horizontal rows of non-shelf-colored pixels
Sometimes shelf corner has random patterns shelf-colored squares 
In most cases the corners "fill in" after the rest of the shelf is shown (looks like pieces of the corners are painted a few frames after the shelf is un-hid).

What is the impact to the user, and is there a workaround? If so, what is
it?

Strange looking shelf.

Related b/114292045
Related feedback/report/85646412323