11 files declare their use of RequestException in Zircon Profile 8

Client.php in vendor/fabpot/goutte/Goutte/Client.php

ClientTest.php in vendor/fabpot/goutte/Goutte/Tests/ClientTest.php

CurlFactory.php in vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php

DefaultFetcher.php in core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php

Contains \Drupal\aggregator\Plugin\aggregator\fetcher\DefaultFetcher.

install.core.inc in core/includes/install.core.inc

API functions for installing Drupal.

locale.batch.inc in core/modules/locale/locale.batch.inc

Batch process to check the availability of remote or local po files.

Middleware.php in vendor/guzzlehttp/guzzle/src/Middleware.php

OpmlFeedAdd.php in core/modules/aggregator/src/Form/OpmlFeedAdd.php

Contains \Drupal\aggregator\Form\OpmlFeedAdd.

StreamHandler.php in vendor/guzzlehttp/guzzle/src/Handler/StreamHandler.php

system.module in core/modules/system/system.module

Configuration system that lets administrators modify the workings of the site.

UpdateFetcher.php in core/modules/update/src/UpdateFetcher.php

Contains \Drupal\update\UpdateFetcher.