code: func (i *ResourceInstance) findUnusedDeposedKey() DeposedKey {
  	for {
  		key := NewDeposedKey()
  		if _, exists := i.Deposed[key]; !exists {
  			return key
  		}
  		// Spin until we find a unique one. This shouldn't take long, because
  		// we have a 32-bit keyspace and there's rarely more than one deposed
  		// instance.
  	}
  }
docs: // findUnusedDeposedKey generates a unique DeposedKey that is guaranteed not to
  // already be in use for this instance.