Enable options to remap CapsLock whenever an external keyboard is connected.
As per comments #16 and #17 on issue 167237, we will assume that most
external keyboards have a CapsLock key (chromeos external keyboards are
exceptions. However, there's no way to distinguish them at the moment).
This CL enables/disables the CapsLock remapping options in the keyboard
settings whenever there's an external keyboard is connected/disconnected
respectively.
BUG=167237
Review URL: https://codereview.chromium.org/
1188693002
Cr-Commit-Position: refs/heads/master@{#334538}