GitLab

A bit of cleanup:
- Remove unused / duplicate includes
- Remove unused enum
- Remove unused methods
- Remove unnecessary friending of RefCountedThreadSafe<>
- Remove unused data members

Bug: None

Change-Id: I2fb0cecfdd93cfca76177ae391566e3e278f1622
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079526Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745657}