Merge restored accessibility enable state, don't overwrite

We do not want to accidentally disable the user's currently-enabled
accessibility service(s); presumably they turned them on during
setup for a reason.  We now merge the prior + current states rather
than simply replacing the current state with the former.

Bug 19427367

Change-Id: I96eb47df57318c88066c5da6862f23f656639148
2 files changed