Support LocaleLists in ActivityManagerService.

Also add a placeholder method for locale negotiation to LocaleList,
to be filled later.

There is no change in behavior expected by this CL yet. But once we
support setting the first locale to something the system doesn't
support, and implement the locale negotiation, this will cause the
system locale to be set to the first supported locale, instead of
just the default from Settings.

Change-Id: Iec983a5707daffb5bf54eac79ff0856a96631960