Chromium directly includes our .gypi files in its own standalone
tests, hence we need to keep files where it looks for includes.
Previously we had removed the gypi files with the new project
structures.

BUG=angle:568

Change-Id: I2cf87bdd3d9635ca8e58b991b9a3e55e00261851
Reviewed-on: https://chromium-review.googlesource.com/187650Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>