This reverts commit b33030a7.

Reason for revert: We're going to try to get the code in this change
submitted in smaller, more carefully reviewed changes.

Change-Id: I4175f4b297f0e69fb78b11f9dc0bd82f27865be7
Reviewed-on: https://go-review.googlesource.com/32441Reviewed-by: Russ Cox <rsc@golang.org>