Unblocks further return value refactoring for perf.

Bug: angleproject:2738
Change-Id: Ie92aa656736f84b4e4ef6d4ab8e0377ad4afb2af
Reviewed-on: https://chromium-review.googlesource.com/1142955Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>