[Sync] Fix bug where DeviceInfo is missing a backup timestamp
Remove last_synced_time_ member variable from ProfileSyncService. This
variable acted as a cache of the underlying pref. However, it was not
properly cleared in ProfileSyncService::DisableForUser when the
associated pref was cleared. This caused a bug where device info may
not have a backup timestamp.
BUG=427096
Review URL: https://codereview.chromium.org/660023003
Cr-Commit-Position: refs/heads/master@{#301481}
(cherry picked from commit 44d307099fc662e56b57c59f23214a85c2b206b2)
Review URL: https://codereview.chromium.org/690153002
Cr-Commit-Position: refs/branch-heads/2171@{#311}
Cr-Branched-From: 267aeeb8d85c8503a7fd12bd14654b8ea78d3974-refs/heads/master@{#297060}
3 files changed
