Add a trace.

Emit a trace when a new dictionary is copied to LatinIME
successfully, not just when it fails. That will help diagnosing
some problems by being able to ensure this step succeeded
looking at the log.
This does not happen often (like, maybe 3 times at device
activation, and once every few weeks afterwards), so I think
the extra line in the log is more than acceptable.

Change-Id: I1674bc22d950a7be801076c5aa7e8bbebccab14b