[Runtime][Tizen] Initialize NSSInitSingleton ahead when Crosswalk service
starts.

For cold launch (Launch application for the first time), profiling data
shows that render process initialization is blocked by
BrowserThread::IO, who is busy at creating the lazy singleton instance
of NSSInitSingleton with ~120ms time cost. As a result, the parsing and
compositing time of render process are postponed.

This CL moves the NSSInitSingleton initialization logic ahead in
Crosswalk service start function so that render process won't wait too
much time for initialization.

From my test result, it could save the cold launch time with 100+ms
for Tizen Common image and ~50ms for IVI image, on VTC-1010.
Merge pull request #2068 from shaochangbin/move_nssinit

[Runtime][Tizen] Initialize NSSInitSingleton ahead when Crosswalk service starts.