libbinder: binders hold wire protocol version

The libbinder wire protocol version is currently unstable, but we may
stablize it. This adds a version field in the stability token which is
passed around with binder objects, so it doesn't require additional
memory.

Future consideration/direction:
- when starting a transaction, attach a binder to a Parcel object
- when parceling, parcel according to the maximum of (locally
  understood wire protocol, binder wire protocol)
- verify in transact the data parcel has the corresponding binder
- when the server creates a reply parcel, note version which is the
  same as the version used in the data Parcel (we know that whoever
  wrote this transaction can understand this level).
- save binary blobs of known write*/read* data flows, and test that
  Parcel can understand and recreate these blobs after it is versioned.

Bug: 167966510
Test: 'atest binderStabilityTest' - verifies behavior
Test: internally checks version is always set
Change-Id: I9bb5be5b5b7d7255f8387cf690d86a055102f95d

0 files changed, 0 insertions, 0 deletions