We had neglected to reference scope bracket values when
initially constructing the scoped struct name. Fixes the
new WebGL test.

BUG=angle:618

Change-Id: Ie78a8264c9e16c5a6574cecd662adbd5475d6495
Reviewed-on: https://chromium-review.googlesource.com/197040Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>