Ensure fileSystem locks around LookUpChild.
Ensure fileSystem locks around LookUpChild.

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