This is in preparation for storing a pointer to a shared resource use
structure.

Bug: angleproject:2464
Change-Id: I8f4ba1c71de6ad6a27ac06fc8012a0e94267cc16
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1785988
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>