Wraps a std::array and a size parameter to give the std::vector interface
without making allocations.

BUG=angleproject:2435

Change-Id: I7df0be1310446a2f163766149bf631a8692be9ad
Reviewed-on: https://chromium-review.googlesource.com/981267
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>