The GYP syntax would cause problems with the ninja build.

BUG=angle:529

Change-Id: I84a30afc9bd8900535e44f5d5f9d8f766a4686e8
Reviewed-on: https://chromium-review.googlesource.com/186610Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>