Continue using timer.lock to simplify timer operations.
Note the removal of a previous potential deadlock.
(Explained at new line 325, there was a lock inversion
between individual timer locks and the 'timers' lock.)
[This is one CL in a refactoring stack making very small changes
in each step, so that any subtle bugs that we miss can be more
easily pinpointed to a small change.]
Change-Id: I8c9be00d13c6acd171a8aa2882a4fc844498f754
Reviewed-on: https://go-review.googlesource.com/c/go/+/564125 Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>