Editable field handlers must implement the field_name() method

Views field handlers that provide an editable field must implement the field_name() method. This is called by the editable view form to get the key of the form element that corresponds to the field.

Previously, this was set in the definition of the field in hook_views_data(). It suffices to do the following:

  /**
   * Return the name of the entity property this handler controls.
   */
  function field_name() {
    return $this->definition['field_name'];
  }

However, if your handler always works with the same form element name, the method can return a fixed value, allowing the field name to be removed from hook_views_data(). Thus:

  /**
   * Return the name of the entity property this handler controls.
   */
  function field_name() {
    return 'title';
  }