Values:
STATE_UNSPECIFIED (0):
The NasTrial state is unspecified.
REQUESTED (1):
Indicates that a specific NasTrial has been
requested, but it has not yet been suggested by
the service.
ACTIVE (2):
Indicates that the NasTrial has been
suggested.
STOPPING (3):
Indicates that the NasTrial should stop
according to the service.
SUCCEEDED (4):
Indicates that the NasTrial is completed
successfully.
INFEASIBLE (5):
Indicates that the NasTrial should not be attempted again.
The service will set a NasTrial to INFEASIBLE when it's done
but missing the final_measurement.