Weird "dirt" over a PDF file view

[vporton]

Description

Near the bottom of the page 278 of chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/http://www.mathematics21.org/binaries/volume-1.pdf there is something looking like dirt. I attach the image
.

I also attach a copy of the PDF file volume-1.pdf because it is sometimes updated on the server.

Actual result:

Dirt.

Expected result:

No dirt.

Brave version (brave://version info)

Version 0.59.35 Chromium: 72.0.3626.81 (Official Build) (64-bit)

[srirambv]

I cleaned my monitor and checked, no dirt on screen or on document

[bsclifton]

Let's retest this after brave/brave-core#2342 lands