cmd: go get golang.org/x/tools@f9b8da7 and revendor

cmd: go get golang.org/x/tools@f9b8da7 and revendor

go get golang.org/x/tools@f9b8da7 # CL 529915
go mod tidy
go mod vendor

Change-Id: Ib0824e66ab8889bfab438e79bf3f7bb4b4f45879
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/530175
Run-TryBot: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Tim King <taking@google.com>