11 files declare their use of RequestException

DefaultFetcher.php in drupal/core/modules/aggregator/lib/Drupal/aggregator/Plugin/aggregator/fetcher/DefaultFetcher.php
Contains \Drupal\aggregator\Plugin\aggregator\fetcher\DefaultFetcher.
EntityEnclosingRequest.php in drupal/core/vendor/guzzle/http/Guzzle/Http/Message/EntityEnclosingRequest.php
EntityEnclosingRequestInterface.php in drupal/core/vendor/guzzle/http/Guzzle/Http/Message/EntityEnclosingRequestInterface.php
install.core.inc in drupal/core/includes/install.core.inc
API functions for installing Drupal.
locale.batch.inc in drupal/core/modules/locale/locale.batch.inc
Batch process to check the availability of remote or local po files.
OpmlFeedAdd.php in drupal/core/modules/aggregator/lib/Drupal/aggregator/Form/OpmlFeedAdd.php
Contains \Drupal\aggregator\Form\OpmlFeedAdd.
Request.php in drupal/core/vendor/guzzle/http/Guzzle/Http/Message/Request.php
RequestInterface.php in drupal/core/vendor/guzzle/http/Guzzle/Http/Message/RequestInterface.php
system.module in drupal/core/modules/system/system.module
Configuration system that lets administrators modify the workings of the site.
update.fetch.inc in drupal/core/modules/update/update.fetch.inc
Code required only when fetching information about available updates.
xmlrpc.inc in drupal/core/modules/xmlrpc/xmlrpc.inc
Drupal XML-RPC library.