Chrome Version: 72.0.3625.0 (Official Build) canary (64-bit)
OS: macOS 10.14.1 18B75

There are two sets of steps to reproduce:
0. Have full keyboard access on. (System Preferences:Keyboard:Shortcuts:Full Keyboard Access = All controls)
1. Wait for an update to be installed in the background, such that the dots menu gets the “restart to update” menu item. (This is slightly easier if you install, say, yesterday’s canary.)
2. Pick the “restart to update” menu item from the dots menu.
3. A box will appear asking you to confirm.
4. Using the keyboard, tab over to the button for relaunching.
5. Press the space bar, which triggers the button.

Expected behavior: Chrome restarts.

Observed behavior: The “Hold ⌘Q to Quit” overlay appears momentarily and then disappears. Chrome does not restart.

Alternate steps to reproduce. These are easier!

1. Go to chrome://flags.
2. Change something.
3. Focus the RELAUNCH NOW button that appears at the bottom. The easiest way I can offer to do this is to start a drag on the button, but end the drag off the button. An alternative (may require full keyboard access, see step 0 above) is to highlight the text to the left of that button and then press TAB.
4. Press the return key to trigger the button.

Expected behavior: Chrome restarts.

Observed behavior: The “Hold ⌘Q to Quit” overlay appears momentarily and then disappears. Chrome does not restart. However, if the space bar was used instead of the return key, chrome DOES restart.

I think that this is a recent regression, because I restart the canary every day or two using this method, and I never drive with the mouse when the keyboard suffices.