Vulkan: Don't take lock for getLastCompletedQueueSerial getLastCompletedQueueSerial() is simply returning a uint64_t serial number. There is no need to take a mutex lock. This CL uses atomic for mLastCompletedQueueSerial and removed the lock as well as removed the virtual function call. This also avoid the annoyance with mutex lock, that if you call getLastCompletedQueueSerial in places that has other lock held, you may end up with deadlock. This CL avoids that trouble all together other than improves performance. Bug: b/230759914 Change-Id: I9dc688d410e4c6bca7fc70ae4f9fe0c3acc2e005 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3607500 Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>