Add system stubs for API 21.

This jar is from the build server:
- branch git_lmp-release
- build id 3678147
- target sdk_phone_armv7-win_sdk

Note that the SDK was released from a dev branch and build id 1624448 that
has expired already. Assuming that due to SDK finalization process, a jar
generated in the release branch at a later date is still correct.

Bug: 190665366
Test: N/A
Change-Id: Ia5e3c929de57fefe994fb949a7e3ae0436b50043
1 file changed