[Background Sync] Extend expiry of metric.

BackgroundSync.Wakeup.DelayTime is scheduled to stop being recorded
after M75, but we could use some more milestones of this metric as
things are changing in this area. This CL extends it to 77.

Bug: 945555
Change-Id: Ieecab02866322da5deb4885bb8909847c9dfc48e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1536195
Auto-Submit: Mugdha Lakhani <nator@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644292}
1 file changed