This test was added and referenced, but was actually never added to the
list of files to be compiled.  The most recent validation work has been
regarding WebGL.

This test verifies the behavior when different stencil masks are set for
front and back faces, which is unsupported in D3D and disallowed in
WebGL.  In the interest of running the test on all back ends, and that
the validation was modified last to improve WebGL support, the test runs
in WebGL compatibility mode.

Bug: chromium:806557
Change-Id: I7615b9fc18d4203ed342e23881bea6bdd9b3864c
Reviewed-on: https://chromium-review.googlesource.com/c/1306256Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>