diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 1ce4298..5832f12 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -13,6 +13,7 @@
 use Drupal\Core\Routing\RouteMatchInterface;
 use Drupal\Core\Url;
 use Drupal\file\Entity\File;
+use Drupal\file\FileFormTrait;
 use Drupal\file\FileInterface;
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Component\Utility\Unicode;
@@ -674,81 +675,6 @@ function file_cron() {
 }
 
 /**
- * Saves form file uploads.
- *
- * The files will be added to the {file_managed} table as temporary files.
- * Temporary files are periodically cleaned. Use the 'file.usage' service to
- * register the usage of the file which will automatically mark it as permanent.
- *
- * @param array $element
- *   The FAPI element whose values are being saved.
- * @param \Drupal\Core\Form\FormStateInterface $form_state
- *   The current state of the form.
- * @param null|int $delta
- *   (optional) The delta of the file to return the file entity.
- *   Defaults to NULL.
- * @param int $replace
- *   (optional) The replace behavior when the destination file already exists.
- *   Possible values include:
- *   - FILE_EXISTS_REPLACE: Replace the existing file.
- *   - FILE_EXISTS_RENAME: (default) Append _{incrementing number} until the
- *     filename is unique.
- *   - FILE_EXISTS_ERROR: Do nothing and return FALSE.
- *
- * @return array|\Drupal\file\FileInterface|null|false
- *   An array of file entities or a single file entity if $delta != NULL. Each
- *   array element contains the file entity if the upload succeeded or FALSE if
- *   there was an error. Function returns NULL if no file was uploaded.
- */
-function file_save_upload_from_form($element, FormStateInterface $form_state, $delta = NULL, $replace = FILE_EXISTS_RENAME) {
-  // Get all errors set before calling this method. This will also clear them
-  // from $_SESSION.
-  $errors_before = drupal_get_messages('error');
-
-  $upload_location = isset($element['#upload_location']) ? $element['#upload_location'] : FALSE;
-  $upload_name = implode('_', $element['#parents']);
-  $upload_validators = isset($element['#upload_validators']) ? $element['#upload_validators'] : [];
-
-  $result = file_save_upload($upload_name, $upload_validators, $upload_location, $delta, $replace);
-
-  // Get new errors that are generated while trying to save the upload. This
-  // will also clear them from $_SESSION.
-  $errors_new = drupal_get_messages('error');
-  if (!empty($errors_new['error'])) {
-    $errors_new = $errors_new['error'];
-
-    if (count($errors_new) > 1) {
-      // Render multiple errors into a single message.
-      $render_array = [
-        'error' => [
-          '#markup' => t('One or more files could not be uploaded.'),
-        ],
-        'item_list' => [
-          '#theme' => 'item_list',
-          '#items' => $errors_new,
-        ],
-      ];
-      $error_message = \Drupal::service('renderer')->renderPlain($render_array);
-    }
-    else {
-      $error_message = reset($errors_new);
-    }
-
-    $form_state->setError($element, $error_message);
-  }
-
-  // Ensure that errors set prior to calling this method are still shown to the
-  // user.
-  if (!empty($errors_before['error'])) {
-    foreach ($errors_before['error'] as $error) {
-      drupal_set_message($error, 'error');
-    }
-  }
-
-  return $result;
-}
-
-/**
  * Saves file uploads to a new location.
  *
  * The files will be added to the {file_managed} table as temporary files.
@@ -788,209 +714,17 @@ function file_save_upload_from_form($element, FormStateInterface $form_state, $d
  *
  * @deprecated in Drupal 8.3.x, will be removed before Drupal 9.0.0.
  *   This function should not be used for form validation, use
- *   file_save_upload_from_form() instead.
+ *   \Drupal\file\FileFormTrait::fileSaveUpload() instead.
  *
- * @see file_save_upload_from_form()
+ * @see \Drupal\file\FileFormTrait::fileSaveUpload()
  */
 function file_save_upload($form_field_name, $validators = array(), $destination = FALSE, $delta = NULL, $replace = FILE_EXISTS_RENAME) {
-  $user = \Drupal::currentUser();
-  static $upload_cache;
-
-  $all_files = \Drupal::request()->files->get('files', array());
-  // Make sure there's an upload to process.
-  if (empty($all_files[$form_field_name])) {
-    return NULL;
-  }
-  $file_upload = $all_files[$form_field_name];
-
-  // Return cached objects without processing since the file will have
-  // already been processed and the paths in $_FILES will be invalid.
-  if (isset($upload_cache[$form_field_name])) {
-    if (isset($delta)) {
-      return $upload_cache[$form_field_name][$delta];
-    }
-    return $upload_cache[$form_field_name];
-  }
-
-  // Prepare uploaded files info. Representation is slightly different
-  // for multiple uploads and we fix that here.
-  $uploaded_files = $file_upload;
-  if (!is_array($file_upload)) {
-    $uploaded_files = array($file_upload);
+  $errors = [];
+  $files = FileFormTrait::_fileSaveUpload($form_field_name, $validators, $destination, $delta, $replace, $errors);
+  foreach ($errors as $error) {
+    drupal_set_message($error, 'error');
   }
-
-  $files = array();
-  foreach ($uploaded_files as $i => $file_info) {
-    // Check for file upload errors and return FALSE for this file if a lower
-    // level system error occurred. For a complete list of errors:
-    // See http://php.net/manual/features.file-upload.errors.php.
-    switch ($file_info->getError()) {
-      case UPLOAD_ERR_INI_SIZE:
-      case UPLOAD_ERR_FORM_SIZE:
-        drupal_set_message(t('The file %file could not be saved because it exceeds %maxsize, the maximum allowed size for uploads.', array('%file' => $file_info->getFilename(), '%maxsize' => format_size(file_upload_max_size()))), 'error');
-        $files[$i] = FALSE;
-        continue;
-
-      case UPLOAD_ERR_PARTIAL:
-      case UPLOAD_ERR_NO_FILE:
-        drupal_set_message(t('The file %file could not be saved because the upload did not complete.', array('%file' => $file_info->getFilename())), 'error');
-        $files[$i] = FALSE;
-        continue;
-
-      case UPLOAD_ERR_OK:
-        // Final check that this is a valid upload, if it isn't, use the
-        // default error handler.
-        if (is_uploaded_file($file_info->getRealPath())) {
-          break;
-        }
-
-        // Unknown error
-      default:
-        drupal_set_message(t('The file %file could not be saved. An unknown error has occurred.', array('%file' => $file_info->getFilename())), 'error');
-        $files[$i] = FALSE;
-        continue;
-
-    }
-    // Begin building file entity.
-    $values = array(
-      'uid' => $user->id(),
-      'status' => 0,
-      'filename' => $file_info->getClientOriginalName(),
-      'uri' => $file_info->getRealPath(),
-      'filesize' => $file_info->getSize(),
-    );
-    $values['filemime'] = \Drupal::service('file.mime_type.guesser')->guess($values['filename']);
-    $file = File::create($values);
-
-    $extensions = '';
-    if (isset($validators['file_validate_extensions'])) {
-      if (isset($validators['file_validate_extensions'][0])) {
-        // Build the list of non-munged extensions if the caller provided them.
-        $extensions = $validators['file_validate_extensions'][0];
-      }
-      else {
-        // If 'file_validate_extensions' is set and the list is empty then the
-        // caller wants to allow any extension. In this case we have to remove the
-        // validator or else it will reject all extensions.
-        unset($validators['file_validate_extensions']);
-      }
-    }
-    else {
-      // No validator was provided, so add one using the default list.
-      // Build a default non-munged safe list for file_munge_filename().
-      $extensions = 'jpg jpeg gif png txt doc xls pdf ppt pps odt ods odp';
-      $validators['file_validate_extensions'] = array();
-      $validators['file_validate_extensions'][0] = $extensions;
-    }
-
-    if (!empty($extensions)) {
-      // Munge the filename to protect against possible malicious extension
-      // hiding within an unknown file type (ie: filename.html.foo).
-      $file->setFilename(file_munge_filename($file->getFilename(), $extensions));
-    }
-
-    // Rename potentially executable files, to help prevent exploits (i.e. will
-    // rename filename.php.foo and filename.php to filename.php.foo.txt and
-    // filename.php.txt, respectively). Don't rename if 'allow_insecure_uploads'
-    // evaluates to TRUE.
-    if (!\Drupal::config('system.file')->get('allow_insecure_uploads') && preg_match('/\.(php|pl|py|cgi|asp|js)(\.|$)/i', $file->getFilename()) && (substr($file->getFilename(), -4) != '.txt')) {
-      $file->setMimeType('text/plain');
-      // The destination filename will also later be used to create the URI.
-      $file->setFilename($file->getFilename() . '.txt');
-      // The .txt extension may not be in the allowed list of extensions. We have
-      // to add it here or else the file upload will fail.
-      if (!empty($extensions)) {
-        $validators['file_validate_extensions'][0] .= ' txt';
-        drupal_set_message(t('For security reasons, your upload has been renamed to %filename.', array('%filename' => $file->getFilename())));
-      }
-    }
-
-    // If the destination is not provided, use the temporary directory.
-    if (empty($destination)) {
-      $destination = 'temporary://';
-    }
-
-    // Assert that the destination contains a valid stream.
-    $destination_scheme = file_uri_scheme($destination);
-    if (!file_stream_wrapper_valid_scheme($destination_scheme)) {
-      drupal_set_message(t('The file could not be uploaded because the destination %destination is invalid.', array('%destination' => $destination)), 'error');
-      $files[$i] = FALSE;
-      continue;
-    }
-
-    $file->source = $form_field_name;
-    // A file URI may already have a trailing slash or look like "public://".
-    if (substr($destination, -1) != '/') {
-      $destination .= '/';
-    }
-    $file->destination = file_destination($destination . $file->getFilename(), $replace);
-    // If file_destination() returns FALSE then $replace === FILE_EXISTS_ERROR and
-    // there's an existing file so we need to bail.
-    if ($file->destination === FALSE) {
-      drupal_set_message(t('The file %source could not be uploaded because a file by that name already exists in the destination %directory.', array('%source' => $form_field_name, '%directory' => $destination)), 'error');
-      $files[$i] = FALSE;
-      continue;
-    }
-
-    // Add in our check of the file name length.
-    $validators['file_validate_name_length'] = array();
-
-    // Call the validation functions specified by this function's caller.
-    $errors = file_validate($file, $validators);
-
-    // Check for errors.
-    if (!empty($errors)) {
-      $message = array(
-        'error' => array(
-          '#markup' => t('The specified file %name could not be uploaded.', array('%name' => $file->getFilename())),
-        ),
-        'item_list' => array(
-          '#theme' => 'item_list',
-          '#items' => $errors,
-        ),
-      );
-      // @todo Add support for render arrays in drupal_set_message()? See
-      //  https://www.drupal.org/node/2505497.
-      drupal_set_message(\Drupal::service('renderer')->renderPlain($message), 'error');
-      $files[$i] = FALSE;
-      continue;
-    }
-
-    // Move uploaded files from PHP's upload_tmp_dir to Drupal's temporary
-    // directory. This overcomes open_basedir restrictions for future file
-    // operations.
-    $file->setFileUri($file->destination);
-    if (!drupal_move_uploaded_file($file_info->getRealPath(), $file->getFileUri())) {
-      drupal_set_message(t('File upload error. Could not move uploaded file.'), 'error');
-      \Drupal::logger('file')->notice('Upload error. Could not move uploaded file %file to destination %destination.', array('%file' => $file->getFilename(), '%destination' => $file->getFileUri()));
-      $files[$i] = FALSE;
-      continue;
-    }
-
-    // Set the permissions on the new file.
-    drupal_chmod($file->getFileUri());
-
-    // If we are replacing an existing file re-use its database record.
-    // @todo Do not create a new entity in order to update it. See
-    //   https://www.drupal.org/node/2241865.
-    if ($replace == FILE_EXISTS_REPLACE) {
-      $existing_files = entity_load_multiple_by_properties('file', array('uri' => $file->getFileUri()));
-      if (count($existing_files)) {
-        $existing = reset($existing_files);
-        $file->fid = $existing->id();
-        $file->setOriginalId($existing->id());
-      }
-    }
-
-    // If we made it this far it's safe to record this file in the database.
-    $file->save();
-    $files[$i] = $file;
-  }
-
-  // Add files to the cache.
-  $upload_cache[$form_field_name] = $files;
-
-  return isset($delta) ? $files[$delta] : $files;
+  return $files;
 }
 
 /**
@@ -1273,7 +1007,7 @@ function file_managed_file_save_upload($element, FormStateInterface $form_state)
   $files_uploaded = $element['#multiple'] && count(array_filter($file_upload)) > 0;
   $files_uploaded |= !$element['#multiple'] && !empty($file_upload);
   if ($files_uploaded) {
-    if (!$files = file_save_upload_from_form($element, $form_state)) {
+    if (!$files = FileFormTrait::fileSaveUpload($element, $form_state)) {
       \Drupal::logger('file')->notice('The file upload failed. %upload', array('%upload' => $upload_name));
       return array();
     }
diff --git a/core/modules/file/src/FileFormTrait.php b/core/modules/file/src/FileFormTrait.php
new file mode 100644
index 0000000..1554e84
--- /dev/null
+++ b/core/modules/file/src/FileFormTrait.php
@@ -0,0 +1,317 @@
+<?php
+
+namespace Drupal\file;
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\file\Entity\File;
+
+/**
+ * Adds methods to save files to forms.
+ */
+trait FileFormTrait {
+
+  /**
+   * Saves form file uploads.
+   *
+   * The files will be added to the {file_managed} table as temporary files.
+   * Temporary files are periodically cleaned. Use the 'file.usage' service to
+   * register the usage of the file which will automatically mark it as permanent.
+   *
+   * @param array $element
+   *   The FAPI element whose values are being saved.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   * @param null|int $delta
+   *   (optional) The delta of the file to return the file entity.
+   *   Defaults to NULL.
+   * @param int $replace
+   *   (optional) The replace behavior when the destination file already exists.
+   *   Possible values include:
+   *   - FILE_EXISTS_REPLACE: Replace the existing file.
+   *   - FILE_EXISTS_RENAME: (default) Append _{incrementing number} until the
+   *     filename is unique.
+   *   - FILE_EXISTS_ERROR: Do nothing and return FALSE.
+   *
+   * @return array|\Drupal\file\FileInterface|null|false
+   *   An array of file entities or a single file entity if $delta != NULL. Each
+   *   array element contains the file entity if the upload succeeded or FALSE if
+   *   there was an error. Function returns NULL if no file was uploaded.
+   */
+  public static function fileSaveUpload($element, FormStateInterface $form_state, $delta = NULL, $replace = FILE_EXISTS_RENAME) {
+    $upload_location = isset($element['#upload_location']) ? $element['#upload_location'] : FALSE;
+    $upload_name = implode('_', $element['#parents']);
+    $upload_validators = isset($element['#upload_validators']) ? $element['#upload_validators'] : [];
+    $errors = [];
+    $files = static::_fileSaveUpload($upload_name, $upload_validators, $upload_location, $delta, $replace, $errors);
+
+    if (!empty($errors)) {
+      if (count($errors) > 1) {
+        // Render multiple errors into a single message.
+        $render_array = [
+          'error' => [
+            '#markup' => t('One or more files could not be uploaded.'),
+          ],
+          'item_list' => [
+            '#theme' => 'item_list',
+            '#items' => $errors,
+          ],
+        ];
+        $error_message = \Drupal::service('renderer')->renderPlain($render_array);
+      }
+      else {
+        $error_message = reset($errors);
+      }
+      $form_state->setError($element, $error_message);
+    }
+
+    return $files;
+  }
+
+  /**
+   * Saves file uploads to a new location.
+   *
+   * The files will be added to the {file_managed} table as temporary files.
+   * Temporary files are periodically cleaned. Use the 'file.usage' service to
+   * register the usage of the file which will automatically mark it as permanent.
+   *
+   * @param string $form_field_name
+   *   A string that is the associative array key of the upload form element in
+   *   the form array.
+   * @param array $validators
+   *   (optional) An associative array of callback functions used to validate the
+   *   file. See file_validate() for a full discussion of the array format.
+   *   If the array is empty, it will be set up to call file_validate_extensions()
+   *   with a safe list of extensions, as follows: "jpg jpeg gif png txt doc
+   *   xls pdf ppt pps odt ods odp". To allow all extensions, you must explicitly
+   *   set this array to ['file_validate_extensions' => '']. (Beware: this is not
+   *   safe and should only be allowed for trusted users, if at all.)
+   * @param string|false $destination
+   *   (optional) A string containing the URI that the file should be copied to.
+   *   This must be a stream wrapper URI. If this value is omitted or set to
+   *   FALSE, Drupal's temporary files scheme will be used ("temporary://").
+   * @param null|int $delta
+   *   (optional) The delta of the file to return the file entity.
+   *   Defaults to NULL.
+   * @param int $replace
+   *   (optional) The replace behavior when the destination file already exists.
+   *   Possible values include:
+   *   - FILE_EXISTS_REPLACE: Replace the existing file.
+   *   - FILE_EXISTS_RENAME: (default) Append _{incrementing number} until the
+   *     filename is unique.
+   *   - FILE_EXISTS_ERROR: Do nothing and return FALSE.
+   * @param array $errors_to_return
+   *   (optional) Any errors that have occurred whilst uploading the file.
+   *
+   * @return array|\Drupal\file\FileInterface|null|false
+   *   An array of file entities or a single file entity if $delta != NULL. Each
+   *   array element contains the file entity if the upload succeeded or FALSE if
+   *   there was an error. Function returns NULL if no file was uploaded.
+   *
+   * @see file_save_upload()
+   * @see file_save_upload()
+   *
+   * @internal
+   */
+  public static function _fileSaveUpload($form_field_name, $validators = [], $destination = FALSE, $delta = NULL, $replace = FILE_EXISTS_RENAME, &$errors_to_return = []) {
+    $user = \Drupal::currentUser();
+    static $upload_cache;
+
+    $all_files = \Drupal::request()->files->get('files', []);
+    // Make sure there's an upload to process.
+    if (empty($all_files[$form_field_name])) {
+      return NULL;
+    }
+    $file_upload = $all_files[$form_field_name];
+
+    // Return cached objects without processing since the file will have
+    // already been processed and the paths in $_FILES will be invalid.
+    if (isset($upload_cache[$form_field_name])) {
+      if (isset($delta)) {
+        return $upload_cache[$form_field_name][$delta];
+      }
+      return $upload_cache[$form_field_name];
+    }
+
+    // Prepare uploaded files info. Representation is slightly different
+    // for multiple uploads and we fix that here.
+    $uploaded_files = $file_upload;
+    if (!is_array($file_upload)) {
+      $uploaded_files = array($file_upload);
+    }
+
+    $files = array();
+    foreach ($uploaded_files as $i => $file_info) {
+      // Check for file upload errors and return FALSE for this file if a lower
+      // level system error occurred. For a complete list of errors:
+      // See http://php.net/manual/features.file-upload.errors.php.
+      switch ($file_info->getError()) {
+        case UPLOAD_ERR_INI_SIZE:
+        case UPLOAD_ERR_FORM_SIZE:
+          $errors_to_return[] = new TranslatableMarkup('The file %file could not be saved because it exceeds %maxsize, the maximum allowed size for uploads.', ['%file' => $file_info->getFilename(), '%maxsize' => format_size(file_upload_max_size())]);
+          $files[$i] = FALSE;
+          break;
+
+        case UPLOAD_ERR_PARTIAL:
+        case UPLOAD_ERR_NO_FILE:
+          $errors_to_return[] = new TranslatableMarkup('The file %file could not be saved because the upload did not complete.', ['%file' => $file_info->getFilename()]);
+          $files[$i] = FALSE;
+          break;
+
+        case UPLOAD_ERR_OK:
+          // Final check that this is a valid upload, if it isn't, use the
+          // default error handler.
+          if (is_uploaded_file($file_info->getRealPath())) {
+            break;
+          }
+
+        default:
+          // Unknown error.
+          $errors_to_return[] = new TranslatableMarkup('The file %file could not be saved. An unknown error has occurred.', ['%file' => $file_info->getFilename()]);
+          $files[$i] = FALSE;
+          break;
+
+      }
+      // Begin building file entity.
+      $values = [
+        'uid' => $user->id(),
+        'status' => 0,
+        'filename' => $file_info->getClientOriginalName(),
+        'uri' => $file_info->getRealPath(),
+        'filesize' => $file_info->getSize(),
+      ];
+      $values['filemime'] = \Drupal::service('file.mime_type.guesser')->guess($values['filename']);
+      $file = File::create($values);
+
+      $extensions = '';
+      if (isset($validators['file_validate_extensions'])) {
+        if (isset($validators['file_validate_extensions'][0])) {
+          // Build the list of non-munged extensions if the caller provided them.
+          $extensions = $validators['file_validate_extensions'][0];
+        }
+        else {
+          // If 'file_validate_extensions' is set and the list is empty then the
+          // caller wants to allow any extension. In this case we have to remove the
+          // validator or else it will reject all extensions.
+          unset($validators['file_validate_extensions']);
+        }
+      }
+      else {
+        // No validator was provided, so add one using the default list.
+        // Build a default non-munged safe list for file_munge_filename().
+        $extensions = 'jpg jpeg gif png txt doc xls pdf ppt pps odt ods odp';
+        $validators['file_validate_extensions'] = array();
+        $validators['file_validate_extensions'][0] = $extensions;
+      }
+
+      if (!empty($extensions)) {
+        // Munge the filename to protect against possible malicious extension
+        // hiding within an unknown file type (ie: filename.html.foo).
+        $file->setFilename(file_munge_filename($file->getFilename(), $extensions));
+      }
+
+      // Rename potentially executable files, to help prevent exploits (i.e. will
+      // rename filename.php.foo and filename.php to filename.php.foo.txt and
+      // filename.php.txt, respectively). Don't rename if 'allow_insecure_uploads'
+      // evaluates to TRUE.
+      if (!\Drupal::config('system.file')->get('allow_insecure_uploads') && preg_match('/\.(php|pl|py|cgi|asp|js)(\.|$)/i', $file->getFilename()) && (substr($file->getFilename(), -4) != '.txt')) {
+        $file->setMimeType('text/plain');
+        // The destination filename will also later be used to create the URI.
+        $file->setFilename($file->getFilename() . '.txt');
+        // The .txt extension may not be in the allowed list of extensions. We have
+        // to add it here or else the file upload will fail.
+        if (!empty($extensions)) {
+          $validators['file_validate_extensions'][0] .= ' txt';
+          drupal_set_message(new TranslatableMarkup('For security reasons, your upload has been renamed to %filename.', ['%filename' => $file->getFilename()]));
+        }
+      }
+
+      // If the destination is not provided, use the temporary directory.
+      if (empty($destination)) {
+        $destination = 'temporary://';
+      }
+
+      // Assert that the destination contains a valid stream.
+      $destination_scheme = file_uri_scheme($destination);
+      if (!file_stream_wrapper_valid_scheme($destination_scheme)) {
+        $errors_to_return[] = new TranslatableMarkup('The file could not be uploaded because the destination %destination is invalid.', ['%destination' => $destination]);
+        $files[$i] = FALSE;
+        continue;
+      }
+
+      $file->source = $form_field_name;
+      // A file URI may already have a trailing slash or look like "public://".
+      if (substr($destination, -1) != '/') {
+        $destination .= '/';
+      }
+      $file->destination = file_destination($destination . $file->getFilename(), $replace);
+      // If file_destination() returns FALSE then $replace === FILE_EXISTS_ERROR and
+      // there's an existing file so we need to bail.
+      if ($file->destination === FALSE) {
+        $errors_to_return[] = new TranslatableMarkup('The file %source could not be uploaded because a file by that name already exists in the destination %directory.', ['%source' => $form_field_name, '%directory' => $destination]);
+        $files[$i] = FALSE;
+        continue;
+      }
+
+      // Add in our check of the file name length.
+      $validators['file_validate_name_length'] = array();
+
+      // Call the validation functions specified by this function's caller.
+      $errors = file_validate($file, $validators);
+
+      // Check for errors.
+      if (!empty($errors)) {
+        $message = array(
+          'error' => array(
+            '#markup' => t('The specified file %name could not be uploaded.', array('%name' => $file->getFilename())),
+          ),
+          'item_list' => array(
+            '#theme' => 'item_list',
+            '#items' => $errors,
+          ),
+        );
+        // @todo Add support for render arrays in drupal_set_message()? See
+        //  https://www.drupal.org/node/2505497.
+        $errors_to_return[] = \Drupal::service('renderer')->renderPlain($message);
+        $files[$i] = FALSE;
+        continue;
+      }
+
+      // Move uploaded files from PHP's upload_tmp_dir to Drupal's temporary
+      // directory. This overcomes open_basedir restrictions for future file
+      // operations.
+      $file->setFileUri($file->destination);
+      if (!\Drupal::service('file_system')->moveUploadedFile($file_info->getRealPath(), $file->getFileUri())) {
+        $errors_to_return[] = new TranslatableMarkup('File upload error. Could not move uploaded file.');
+        \Drupal::logger('file')->notice('Upload error. Could not move uploaded file %file to destination %destination.', array('%file' => $file->getFilename(), '%destination' => $file->getFileUri()));
+        $files[$i] = FALSE;
+        continue;
+      }
+
+      // Set the permissions on the new file.
+      drupal_chmod($file->getFileUri());
+
+      // If we are replacing an existing file re-use its database record.
+      // @todo Do not create a new entity in order to update it. See
+      //   https://www.drupal.org/node/2241865.
+      if ($replace == FILE_EXISTS_REPLACE) {
+        $existing_files = entity_load_multiple_by_properties('file', array('uri' => $file->getFileUri()));
+        if (count($existing_files)) {
+          $existing = reset($existing_files);
+          $file->fid = $existing->id();
+          $file->setOriginalId($existing->id());
+        }
+      }
+
+      // If we made it this far it's safe to record this file in the database.
+      $file->save();
+      $files[$i] = $file;
+    }
+
+    // Add files to the cache.
+    $upload_cache[$form_field_name] = $files;
+
+    return isset($delta) ? $files[$delta] : $files;
+  }
+
+}
diff --git a/core/modules/file/src/Tests/SaveUploadFormTest.php b/core/modules/file/src/Tests/SaveUploadFormTest.php
index c795120..3714b97 100644
--- a/core/modules/file/src/Tests/SaveUploadFormTest.php
+++ b/core/modules/file/src/Tests/SaveUploadFormTest.php
@@ -5,11 +5,11 @@
 use Drupal\file\Entity\File;
 
 /**
- * Tests the file_save_upload_from_form() function.
+ * Tests the \Drupal\file\FileFormTrait::fileSaveUpload() function.
  *
  * @group file
  *
- * @see file_save_upload_from_form()
+ * @see \Drupal\file\FileFormTrait::fileSaveUpload()
  */
 class SaveUploadFormTest extends FileManagedTestBase {
 
diff --git a/core/modules/file/tests/file_test/src/Form/FileTestSaveUploadFromForm.php b/core/modules/file/tests/file_test/src/Form/FileTestSaveUploadFromForm.php
index d06f53f..0edf5a2 100644
--- a/core/modules/file/tests/file_test/src/Form/FileTestSaveUploadFromForm.php
+++ b/core/modules/file/tests/file_test/src/Form/FileTestSaveUploadFromForm.php
@@ -5,12 +5,14 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\State\StateInterface;
+use Drupal\file\FileFormTrait;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * File test form class.
  */
 class FileTestSaveUploadFromForm extends FormBase {
+  use FileFormTrait;
 
   /**
    * Stores the state storage service.
@@ -144,7 +146,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
     $form['file_test_upload']['#upload_location'] = $destination;
 
     drupal_set_message($this->t('Number of error messages before file_save_upload_from_form(): @count.', ['@count' => count(drupal_get_messages('error', FALSE))]));
-    $file = file_save_upload_from_form($form['file_test_upload'], $form_state, 0, $form_state->getValue('file_test_replace'));
+    $file = $this->fileSaveUpload($form['file_test_upload'], $form_state, 0, $form_state->getValue('file_test_replace'));
     drupal_set_message($this->t('Number of error messages after file_save_upload_from_form(): @count.', ['@count' => count(drupal_get_messages('error', FALSE))]));
 
     if ($file) {
diff --git a/core/modules/locale/src/Form/ImportForm.php b/core/modules/locale/src/Form/ImportForm.php
index 60b2d50..f344873 100644
--- a/core/modules/locale/src/Form/ImportForm.php
+++ b/core/modules/locale/src/Form/ImportForm.php
@@ -5,6 +5,7 @@
 use Drupal\Core\Form\FormBase;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\file\FileFormTrait;
 use Drupal\language\ConfigurableLanguageManagerInterface;
 use Drupal\language\Entity\ConfigurableLanguage;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -13,6 +14,7 @@
  * Form constructor for the translation import screen.
  */
 class ImportForm extends FormBase {
+  use FileFormTrait;
 
   /**
    * Uploaded file entity.
@@ -155,7 +157,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function validateForm(array &$form, FormStateInterface $form_state) {
-    $this->file = file_save_upload_from_form($form['file'], $form_state, 0);
+    $this->file = $this->fileSaveUpload($form['file'], $form_state, 0);
 
     // Ensure we have the file uploaded.
     if (!$this->file) {
diff --git a/core/modules/system/src/Form/ThemeSettingsForm.php b/core/modules/system/src/Form/ThemeSettingsForm.php
index 5dbc411..43cbc8d 100644
--- a/core/modules/system/src/Form/ThemeSettingsForm.php
+++ b/core/modules/system/src/Form/ThemeSettingsForm.php
@@ -6,6 +6,7 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\Element;
 use Drupal\Core\StreamWrapper\PublicStream;
+use Drupal\file\FileFormTrait;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesserInterface;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
@@ -364,14 +365,14 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
 
     if ($this->moduleHandler->moduleExists('file')) {
       // Check for a new uploaded logo.
-      $file = file_save_upload_from_form($form['logo']['settings']['logo_upload'], $form_state, 0);
+      $file = FileFormTrait::fileSaveUpload($form['logo']['settings']['logo_upload'], $form_state, 0);
       if ($file) {
         // Put the temporary file in form_values so we can save it on submit.
         $form_state->setValue('logo_upload', $file);
       }
 
       // Check for a new uploaded favicon.
-      $file = file_save_upload_from_form($form['favicon']['settings']['favicon_upload'], $form_state, 0);
+      $file = FileFormTrait::fileSaveUpload($form['favicon']['settings']['favicon_upload'], $form_state, 0);
       if ($file) {
         // Put the temporary file in form_values so we can save it on submit.
         $form_state->setValue('favicon_upload', $file);