Vulkan: track attributes in client memory. To support indexed draws it's useful to have a cheap query for the presence of vertex attribute data in client memory. This patch adds a bit mask to keep track of such attributes. It also lets us simplify VertexArrayVk::streamVertexData() slightly. BUG=angleproject:1683 Change-Id: I871bfb885112650b025e110c383db3c391eafb90 Reviewed-on: https://chromium-review.googlesource.com/947927 Commit-Queue: Frank Henigman <fjhenigman@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>