misc/chrome/gophertool: update for the git/gerrit transition

Change-Id: I7b9601ae6e1cfb18ef79a7b189aa7e689c0fe942
Reviewed-on: https://go-review.googlesource.com/1621
Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>