Add script for landing CLs on behalf of external authors.
Add script for landing CLs on behalf of external authors.

Currently there is no easy way for external authors to directly contribute
to the DOM Distiller repository.

This CL adds a helpful script for members of the DOM Distiller project to
land CLs on behalf of external authors.

BUG=
R=cjhopman@chromium.org, wychen@chromium.org

Review URL: https://codereview.chromium.org/1052803002

dalmirdasilva/dom-distiller,dalmirdasilva/dom-distiller,dalmirdasilva/dom-distiller,dalmirdasilva/dom-distiller,dalmirdasilva/dom-distiller