In a ToT Chrome build running on Chrome OS with --mash, I don't see any way to switch the input method at the login screen; it's always using QWERTY.

In non-mash, you can use either the system tray or the Ctrl+Shift+Space accelerator to cycle between a few keyboard layouts, including QWERTY, Dvorak, and Colemak. We remember the previous selection, although I'm not sure if there's a global setting for it or if we're hoisting it up from the currently-selected user's prefs.

It looks like this is possibly also broken after logging in; an account that I previously configured to use Dvorak is using QWERTY instead. I think the browser process has crashed, though, which probably doesn't help matters.