Reproduced on kevin like this:

Odd graphics glitch, reproducible like this:

0. Be in a resolution like 1500 x 1000 that is non-1.0 and non-2.0 scaling factor.

1. Open a browser window.  Make sure it's exactly aligned with the top-right of the screen but otherwise not full screen.

2. Open a gmail chat window.

3. Put the gmail chat window to the left of the browser window but not aligned to the top of the screen.

Observe: strange black covers the right side of the chat window.  Goes away when you click on the chat window.

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Feedback report: https://feedback.corp.google.com/#/Report/16273822233