GitLab

This makes SessionsSyncManager smaller, which I believe justifies the
change. But actually, it is motivated by upcoming changes in sessions
sync code, where a new implementation will be introduced for USS. We
anticipate the need for the very same logic to track global ID mappings
for user events.

Bug: 681921
Change-Id: I0dcd1858c602a2cc167ca3ac0e2e9d55d072c291
Reviewed-on: https://chromium-review.googlesource.com/916763
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Nicolas Zea <zea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536983}