Use angle::Result in front-end (Part 7) Refactors the gl::FenceNV and gl::Sync classes. Bug: angleproject:2491 Change-Id: I0fe73d1ccf5407f460e173a3061735b330a88511 Reviewed-on: https://chromium-review.googlesource.com/c/1289712 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>