Refactor sync EPs (plus one extra). More entry point validation refactor for auto-gen. BUG=angleproject:747 Change-Id: I9462a28838df3f265e1401f66c838cc5a73d511f Reviewed-on: https://chromium-review.googlesource.com/636517 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>