Vulkan: Only access ContextVk in EGLSync if asked to flush Bug: b/362604439 Change-Id: Ifec413628de88e9048e8134c2c5e9497970f358c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5828261 Reviewed-by: Igor Nazarov <i.nazarov@samsung.com> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>