Add some more options for autocomplete key

According to https://support.google.com/chromebook/answer/183101?hl=en,
Chromebook uses Ctrl-Space as keyboard switch. This makes autocomplete
unusable on this and other systems that use this shortcut. We should offer
alternative shortcuts for users of these systems.

Bug: T203320
Change-Id: I4da2a05a8ba14bfa4edee26453e2e8bc42f50f49