GitLab

This CL completes the conversion of GCM's production code to talk
to IdentityManager rather than legacy signin classes by converting
AccountTracker. The GCMAccountTracker unittest remains to be fully
converted away from the legacy signin classes; this will be done in a
followup CL.

TBR=rohitrao@chromium.org, rockot@chromium.org

Bug: 809923
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I1513b33850f52b532d83ac389a78464b68ed1a45
Reviewed-on: https://chromium-review.googlesource.com/1148200Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580101}