HTML headers can only be sent via JS, we need this change to allow
secure POST form submission.
The form itself will have a hidden "input" tag with the XSRF token in it. This
is how other framework do it as well - see
https://en.wikipedia.org/wiki/Cross-site_request_forgery#Synchronizer_token_pattern
This is in preparation for the OT&E setup page, which will be a simple form
with a "submit" button, so using JS for it is overkill.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=226178070
