GitLab

This was usually already an origin, and is used for security-sensitive
purposes such as de-duplicating permission bubble requests (see also
https://codereview.chromium.org/1610753002), so renaming it to GetOrigin
to be explicit.

BUG=577313

Review URL: https://codereview.chromium.org/1637913002

Cr-Commit-Position: refs/heads/master@{#371795}