This keeps the target definition cleaner and will enable GN, if we
ever get to that point.

BUG=angleproject:998

Change-Id: I8692c93155a6bada9b1b0c05a1dd34af64a3b400
Reviewed-on: https://chromium-review.googlesource.com/280992Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>