The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a09fa45af4156c64d416a6448f23025bd85d5721

commit a09fa45af4156c64d416a6448f23025bd85d5721
Author: Blake O'Hare <blakeo@chromium.org>
Date: Fri Oct 13 04:19:58 2017

Change ModifierKey enum to enum class

This is a follow-up on the TODO left by crrev.com/c/683574

After adding a helper function to one of the unit tests, the
proliferation of static_cast<int>(...) is relatively modest.

Bug:  772313 
Change-Id: Ieefea5443263740e1c5bcff53cdedad400bf33e5
Reviewed-on: https://chromium-review.googlesource.com/716616
Reviewed-by: Satoru Takabayashi <satorux@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Blake O'Hare <blakeo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508586}
[modify] https://crrev.com/a09fa45af4156c64d416a6448f23025bd85d5721/ash/system/tray_caps_lock.cc
[modify] https://crrev.com/a09fa45af4156c64d416a6448f23025bd85d5721/chrome/browser/chromeos/events/event_rewriter_unittest.cc
[modify] https://crrev.com/a09fa45af4156c64d416a6448f23025bd85d5721/chrome/browser/chromeos/preferences.cc
[modify] https://crrev.com/a09fa45af4156c64d416a6448f23025bd85d5721/chrome/browser/ui/webui/chromeos/keyboard_overlay_ui.cc
[modify] https://crrev.com/a09fa45af4156c64d416a6448f23025bd85d5721/ui/chromeos/events/event_rewriter_chromeos.cc
[modify] https://crrev.com/a09fa45af4156c64d416a6448f23025bd85d5721/ui/chromeos/events/modifier_key.h