This will make implementing arrays of arrays simpler for struct
members as well. Similar refactoring was already done for other types
of array declarations.

BUG=angleproject:2125
TEST=angle_unittests

Change-Id: I0483c3a7c006d37090c7c972cb3d7763d3909c8f
Reviewed-on: https://chromium-review.googlesource.com/739824Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>