net/http, strings, bytes: fix http race, revert part of Reader behavior change
I fixed this data race regression in two ways: in net/http itself, and also
partially reverting the change from https://golang.org/cl/
77580046 .
Previously a Read from a strings.Reader or bytes.Reader returning 0 bytes
would not be a memory write. After
77580046 it was. This reverts that back
in case others depended on that. Also adds tests.
Fixes #7856
LGTM=ruiu, iant
R=iant, ruiu
CC=golang-codereviews, gri
https://golang.org/cl/
94740044