UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3153.4 Safari/537.36

Example URL:
Any PDF document; chrome://settings/ (toggles); any YouTube video with dark polymer mode

Steps to reproduce the problem:
Open:
* any PDF document
* chrome://settings/
* a YouTube video in dark polymer mode

What is the expected behavior?

What went wrong?
Some unusual black squares appear around certain elements.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? Yes 

Does this work in other browsers? Yes

Chrome version: 61.0.3153.4  Channel: dev
OS Version: OS X 10.12.5
Flash Version:
 

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