Simplify (and defuse) the filter skipping code

  if (in_array(FilterInterface::TYPE_HTML_RESTRICTOR, $filter_types_to_skip)) {
    $filter_types_to_skip = array_diff($filter_types_to_skip, array(FilterInterface::TYPE_HTML_RESTRICTOR));
  }
// ...
  foreach ($filters as $filter) {
    // If necessary, skip filters of a certain type.
    if (in_array($filter->getType(), $filter_types_to_skip)) {
      continue;
    }
    if ($filter->status) {
      $text = $filter->prepare($text, $langcode);
    }
  }

When someone puts in a $filter->getType == somewhere and I put in FilterInterface::TYPE_HTML_RESTRICTOR . 'foo' to be skipped then things will really go sideways: array_diff compares on (string) $elem1 === (string) $elem2 so "1foo" !== "1" but sure as hell "1foo" == 1! Do you want to audit everything that comes into contact with the html restrictor type to not use the == sign? Let's not bear traps into core, mkay?

  function _filter_needs_applying($filter, $filter_types_to_skip) {
    $type = $filter->getType();
    return $filter->status && ($type == FilterInterface::TYPE_HTML_RESTRICTOR || !in_array($type, $filter_types_to_skip));
  }
  foreach ($filters as $filter) {
    if (_filter_needs_applying($filter)) {
      $text = $filter->prepare($text, $langcode);
    }

Use a closure if you like that better. Same loop for process.