GitLab

- Remove PROCESS_INVITE_FAILED event that was handled identically to
PROCESS_INVITE event.
- Use CustomEvent instead of Event for all events

Bug: None
Change-Id: I9de2723779267dc0e8b8d195337b89d9aeb5ca8f
Reviewed-on: https://chromium-review.googlesource.com/c/1395178
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619886}