Remove uses of std::unique_ptr in perftests. This is disallowed in Chromium because it isn't currently portable. We can put it back later if the rules change. BUG=angleproject:956 Change-Id: I5be28590f494719b8cc995739dde26726283fced Reviewed-on: https://chromium-review.googlesource.com/262777 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Brandon Jones <bajones@chromium.org>