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This CL
1 - Adds language struct to the proto consisting of name, native text,
  and locale.
2 - VideoTutorialService will still store the preferred locale in a
  pref which will be used as a key when iterating through the
  supporting languages.
3 - Removes the checked in strings for languages

TODO : Change server side proto

Bug: 1132161
Change-Id: I1483903e0615714aa790b6af1fbfaa4c6637c802
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2429979
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811131}