code: func touch(state *messages.InstanceCache, instanceID string, now time.Time) {
  	entry := state.Entries[instanceID]
  	if entry == nil {
  		entry = &messages.InstanceCache_Entry{}
  		if state.Entries == nil {
  			state.Entries = map[string]*messages.InstanceCache_Entry{}
  		}
  		state.Entries[instanceID] = entry
  	}
  	entry.LastAccess = google.NewTimestamp(now)
  }
docs: // touch updates/adds last access time for an instance.