The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3

commit 41f4c374bc3e2b49c32c57d2b661dbffbeff40c3
Author: Marc-Antoine Courteau <macourteau@chromium.org>
Date: Mon Dec 18 19:33:07 2017

Adds the SpellcheckEnabled policy.

Screenshot: https://drive.google.com/file/d/1NyhlzNdW0eX5wjgZsczfGb_Id8Tzoiqu/view?usp=sharing

Bug:  793927 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: If77b933876d7cdd30581f4685d6187565ced334f
Reviewed-on: https://chromium-review.googlesource.com/826185
Commit-Queue: Marc-Antoine Courteau <macourteau@chromium.org>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524763}
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/app/settings_strings.grdp
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/browser/extensions/api/settings_private/prefs_util.cc
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/browser/policy/configuration_policy_handler_list_factory.cc
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/browser/resources/settings/languages_page/languages_page.html
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/browser/resources/settings/languages_page/languages_page.js
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/browser/spellchecker/spellcheck_language_policy_handler.cc
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/browser/ui/webui/settings/md_settings_localized_strings_provider.cc
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/test/data/policy/policy_test_cases.json
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/test/data/webui/settings/fake_language_settings_private.js
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/chrome/test/data/webui/settings/languages_page_tests.js
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/components/policy/resources/policy_templates.json
[modify] https://crrev.com/41f4c374bc3e2b49c32c57d2b661dbffbeff40c3/tools/metrics/histograms/enums.xml

This will be available in Chrome 65.

Verified fixed. This policy is available in YAPS and allows to enable/disable spellchecking. Tested in M-65 and M-66.

Chrome OS: 10323.63.0
Chrome: 65.0.3325.197
Device: Nasher360

Chrome OS: 10452.30.0
Chrome: 66.0.3359.67
Device: Robo360