The in-progress WASM port does not yet have sufficient automatic
testing performed against it, so these errors slipped through when
adding the new Fetch API backed http.Roundtripper.

Updates #25506

Change-Id: I84c5832452e3e6067a02d926f67d01aaca66b837
GitHub-Last-Rev: 064062b5fd256e7fce961a13a8ac00a135f60221
GitHub-Pull-Request: golang/go#25714
Reviewed-on: https://go-review.googlesource.com/116076Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>