html: use sync.OnceValues instead of var once sync.Once
Simplify populateMaps with sync.OnceValues.
Change-Id: Id52e6e1623c621b8d51e11fecbe3f1fab1e74eb4
GitHub-Last-Rev:
3cf736ae299f14ece401d218d68c3c8870e0cf5a
GitHub-Pull-Request: golang/go#69946
Reviewed-on: https://go-review.googlesource.com/c/go/+/621255
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>