Adds block type-specific submission handling for the block form.
Note that this method takes the form structure and form state arrays for the full block configuration form as arguments, not just the elements defined in BlockBase::blockForm().
array $form: The form definition array for the full block configuration form.
array $form_state: An array containing the current state of the configuration form.
Overrides BlockBase::blockSubmit
\Drupal\block\BlockBase::blockForm()
\Drupal\block\BlockBase::blockValidate()
\Drupal\block\BlockBase::submit()
public function blockSubmit($form, &$form_state) {
$this->configuration['display_message'] = $form_state['values']['display_message'];
}