R=Go1.13

Updates #12711.
Updates #19308.
Updates #28493.
Updates #29008.

Change-Id: Icd25aa7f6e18ed671ea6cf2b1b292899daf4b1a5
Reviewed-on: https://go-review.googlesource.com/c/160018Reviewed-by: Russ Cox <rsc@golang.org>