Chrome Version: 70.0.3507.0
OS: OSX 10.13.6, CrOS, Win
MR: 7018.730.0.0

What steps will reproduce the problem?
(1) Click on the Cast icon in the toolbar to open the dialog.
(2) Press tab key to move focus.
(3) Press enter on a Cast target.
(4) Press tab key to attempt to focus on Cast button.

What is the expected result? User should be able to use tab key to move from device list to the Cast and Sources button in the dialog.

What happens instead? Focus never leaves the list of devices.

Note that when the dialog is first opened, focus is placed on the Cast button. But if tab is pressed, it's moved to the device list.