Chrome: 70.0.3514.0
OS: OSX 10.13.6, CrOS, Win
MR: 7018.806.0.0

What steps will reproduce the problem?
(1) Click the Cast icon in toolbar to open dialog.
(2) Try to identify visually which element has focus.
(3) Press enter key.

What is the expected result? In #2, it looks like the first device has focus, since it's highlighted in gray (or if there's already an active route, then it is highlighted in gray.) So pressing enter should just re-select it, or do nothing.

What happens instead? The Cast button is pressed.

Note that there's a bug where you can't tab through the Sources and Cast button. But you can if a screen reader is enabled, and then it's clear there is no UI indicating focus on those buttons.