This is a reland of a32f98e6

Original change's description:
> Expand variables in gclient flattened output.
>
> Bug: 848990
> Change-Id: I0ad7e4f965973edbc5a335bd30f9cbd7b04abff2
> Reviewed-on: https://chromium-review.googlesource.com/1085996
> Reviewed-by: Michael Moss <mmoss@chromium.org>
> Reviewed-by: Aaron Gable <agable@chromium.org>
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

Tbr: agable@chromium.org
Bug: 848990
Change-Id: I7843544b79b2ab7e2046c187d13ea3eb65fc1b7d
Reviewed-on: https://chromium-review.googlesource.com/1085975Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>