Refactored LookUpChild.
Refactored LookUpChild.

jacobsa/ratelimit,GoogleCloudPlatform/gcsfuse,kahing/gcsfuse,BanzaiMan/gcsfuse,GoogleCloudPlatform/gcsfuse,GoogleCloudPlatform/gcsfuse,jacobsa/timeutil,BanzaiMan/gcsfuse,mbrukman/gcsfuse