This CL includes changes from:

https://golang.org/cl/13929
https://golang.org/cl/13854

Part of fixing https://golang.org/issue/12015

Change-Id: I62e00e165d97d2349c89a783aed7fcbe9e0abd34
Reviewed-on: https://go-review.googlesource.com/14016
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>