[Media Controls] Localize CC to S by locale

Use a "S" icon for the captions button by default
except for "en", "en-US", "es-419" and "pt-BR" which
should continue to use the CC icon.

I added some clarification about which locales in the
bug since there was some regions that were not locales
supported by Chrome.

BUG=353120

Change-Id: I41e05058a6b1589eddce0605d39272b4dd965248
Reviewed-on: https://chromium-review.googlesource.com/1134480
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574639}
4 files changed