Several SafeMarkup methods removed from Core, causing Fatal PHP errors

The SafeMarkup::xssFilter() method has been removed from Drupal 8 Core (see: https://www.drupal.org/node/2549395 ), as well as several other SafeMarkup methods. This is causing fatal PHP errors when using the Features UI on the Dev branch of D8 (and future beta releases).

All calls to the following methods need to be replaced:

• SafeMarkup::replace() - there is no direct replacement for this. A generic function to handle this was problematic - code that needs to do something like this must handle the problem itself. See views_pre_render_views_form_views_form().
• SafeMarkup::xssFilter() - see https://www.drupal.org/node/2549395
• SafeMarkup::placeholder() - there is no direct replacement for this. Use \Drupal\Component\Utility\SafeMarkup::format() with $args = ['%placeholder' => 'thing to be placeholdered']
• SafeMarkup::escape() - The same as SafeMarkup::checkPlain() applies here: rely on Twig's auto-escaping feature, use the #plain_text key in a render array. If neither are those are possible and you require explicit escaping, use Html::escape().
  Note that SafeMarkup::escape() only used to escape strings that were marked as unsafe, so Html::escape() is not a direct equivalent. Use SafeMarkup::isSafe() if you want to check for safeness before escaping.
• SafeMarkup::set() - use one of the strategies in https://www.drupal.org/node/2311123

Note also that SafeMarkup::checkPlain() has been deprecated, and is scheduled to be removed before 8.0.0 is released.