When querying across two points in time this describes the change
between the two points: ADDED, REMOVED, or ACTIVE. If there was no
compare_duration supplied in the request the state should be: UNUSED
Values:
STATE_UNSPECIFIED (0):
Unspecified state.
UNUSED (1):
Request did not specify use of this field in
the result.
ADDED (2):
Asset was added between the points in time.
REMOVED (3):
Asset was removed between the points in time.
ACTIVE (4):
Asset was active at both point(s) in time.