Add maximum timestamp to the payload.
Added a new field max_timestamp in the protobuf, from now on
update_engine will reject any payload without this field.
If the OS build timestamp is newer than the max_timestamp, the payload
will also be rejected to prevent downgrade.
Bug: 36232423
Test: update_engine_unittests
Merged-In: Ib20f5f35aaf41165013bada02bc8720917358237
Change-Id: Ib20f5f35aaf41165013bada02bc8720917358237
(cherry picked from commit 5011df680621eb477cad8b34f03fba5b542cc2f9)
(cherry picked from commit ccb01b2a3beb94094388de806bc15b210ebe8b11)
18 files changed