expvar: convert f to atomic type
For #53821
Change-Id: I2e7c5376e6ca3e3dbb2f92ad771aed62fca8b793
GitHub-Last-Rev:
b67ddf81ecec1892871044fbcb143ca4256ebc55
GitHub-Pull-Request: golang/go#54864
Reviewed-on: https://go-review.googlesource.com/c/go/+/428195
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>