Vulkan: Add ContextVk::onFramebufferBoundary() function This makes a more formal API to track frame boundary. Also adds a uint32_t mCurrentFrameCount to track the total number of frames rendered so that we could use for heuristic purpose. Bug: angleproject:372268711 Change-Id: I153497403ed0d8fde18f1786186ce600df60c514 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6022549 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Charlie Lao <cclao@google.com>