Vulkan: Skip empty submissions A number of places in ANGLE perform an implicit flush; eglSwapBuffers(), glFenceSync() etc. Sometimes these flushes are unnecessary because there is nothing to submit. Additionally, an application may unnecessarily issue glFlush() with nothing recorded. In this change, empty command buffers are automatically not submitted, optimizing these unnecessary flushes away. Bug: angleproject:7084 Change-Id: Iecb865b6b9ef8045dfecda7b5221874f7031b42e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3600837 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>