TBR: jni: Prepare all repos for open-sourcing.

The CONTRIBUTING file is added to all repos, and also added
to the jiri-copyright tool so that repos can be automatically
checked and fixed.

I've run jiri copyright fix against all repos to fix up
outstanding issues.

MultiPart: 4/23

Change-Id: I3465c0d9937fdbe6a390632b67d847057afeb3dd
2 files changed