This will be needed outside of InitializeVariables when removing
unreferenced variables is added. Named struct type declarations
cannot be pruned as easily as they might be referenced later.

BUG=angleproject:2166
TEST=angle_unittests

Change-Id: If1462abe67e62ae19bde97de3c8f3d15e99ae9ea
Reviewed-on: https://chromium-review.googlesource.com/771790Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>