Add Apache 2.0 license.

Change-Id: I5fd6299aa8e7d2edd78f430d8f09cb13f47fa99d
Reviewed-on: https://gerrit-review.googlesource.com/93276
Reviewed-by: Patrick Hiesel <hiesel@google.com>
Reviewed-by: ekempin <ekempin@google.com>
Tested-by: ekempin <ekempin@google.com>