Helper interface for nsIProfileMigrator.
@provider Toolkit (Startup code)
@client Application (Profile-migration code)
@obtainable nsIProfileMigrator.migrate
Do profile-startup by setting NS_APP_USER_PROFILE_50_DIR in the directory
service and notifying the profile-startup observer topics.
The root directory of the semi-current profile, during profile migration.
After nsIProfileMigrator.migrate has returned, this object will not be
useful.