This will faciliate the MANGLE implementation.

BUG=angle:732

Change-Id: I0e4d569667e03305c9cca8d7c23154c70fb71eeb
Reviewed-on: https://chromium-review.googlesource.com/213854Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>