For capture, we'd ideally like to know the return value of a function
when we capture it. The first step will be to intercept the return
value instead of returning directly.

Bug: angleproject:3611
Change-Id: I68c21aea323a71c6a9f1be613862158a37e2beae
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1706560Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>