Reland "Add remoting FTL API key"

This is a reland of c0cf050da7f33e4437a7616935a2d5ca9ae50aa2.

It also fixes a bug that the GetRemotingFtlAPIKey function is mistakenly
named GetFtlAPIKey in the CC file.

Original change's description:
> Add remoting FTL API key
>
> Add API key for remoting to use during the signaling process. Note that
> this key is only used by Chrome Remote Desktop and will not be used in
> the Chrome browser.
>
> Internal CL: https://chrome-internal-review.googlesource.com/c/chrome/google_apis/internal/+/831973
>
> Bug: 927962
> Change-Id: Iecfa48aebe1078a4a0c747f42711000d9155fc3f
> Reviewed-on: https://chromium-review.googlesource.com/c/1450409
> Reviewed-by: Joe Downing <joedow@chromium.org>
> Reviewed-by: Roger Tawa <rogerta@chromium.org>
> Auto-Submit: Yuwei Huang <yuweih@chromium.org>
> Commit-Queue: Roger Tawa <rogerta@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#630352}

Bug: 927962
Change-Id: I04c995d4348ef42de8a72c8c4abd5cff60cda1cd
Reviewed-on: https://chromium-review.googlesource.com/c/1461551
Reviewed-by: Roger Tawa <rogerta@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631828}
2 files changed