function validateExplicitKey(component, parentType) {
  if (component._store.validated || component.props.key != null) {
    return;
  }
  component._store.validated = true;

  warnAndMonitorForKeyUse(
    'react_key_warning',
    'Each child in an array should have a unique "key" prop.',
    component,
    parentType
  );
}
Warn if the component doesn't have an explicit key assigned to it.
This component is in an array. The array could grow and shrink or be
reordered. All children that haven't already been validated are required to
have a "key" property assigned to it.

@internal
@param {ReactComponent} component Component that requires a key.
@param {*} parentType component's parent's type.