Ozone null pointer checks. Check for null pointers so DisplayOzone::terminate() doesn't crash when DisplayOzone::initialize() wasn't completely successful. BUG=angleproject:1419 Change-Id: I70e994490a7282083d5289e6c35b077676688b65 Reviewed-on: https://chromium-review.googlesource.com/354700 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Frank Henigman <fjhenigman@chromium.org>