fat fingers - did not intend to submit.
depends on the Unmarshaler CL anyway.

««« original CL description
encoding/xml: add, support Marshaler interface

See golang.org/s/go12xml for design.

Fixes #2771.
Fixes #4169.
Fixes #5975.
Fixes #6125.

R=golang-dev, iant, dan.kortschak
CC=golang-dev
https://golang.org/cl/12603044
»»»

TBR=golang-dev
CC=golang-dev
https://golang.org/cl/12918043