That way, we don't have to explicitly disable Wimplicit-fallthrough
for these targets, and when we add new warnings to chromium_code in
the future, these targets won't need any special attention.

Like https://chromium-review.googlesource.com/c/chromium/src/+/905222

Bug: 807632
Change-Id: I3a605dd3ef9ed7d8cfe9e36964c3433040bfc330
Reviewed-on: https://chromium-review.googlesource.com/922503Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>