Vulkan: Fix EGL_EXT_buffer_age with single buffered surface The specification: 4) What is the buffer age of a single buffered surface? RESOLVED: 0. This falls out implicitly from the buffer age calculations, which dictate that a buffer's age starts at 0, and is only incremented by frame boundaries. Since frame boundary functions do not affect single buffered surfaces, their age will always be 0. Test: angle_end2end_tests --gtest_filter=EGLBufferAgeTest.SingleBuffer* Bug: angleproject:3529 Change-Id: Iab5da26d1bce56d928398cc250d900465fc5d261 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5675986 Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Igor Nazarov <i.nazarov@samsung.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>