Refactor setting the input layout and vertex buffers separately. BUG=angle:613 Change-Id: Id2ecfc215ef65164cb9ee8bfbad168e9af658386 Reviewed-on: https://chromium-review.googlesource.com/197722 Tested-by: Nicolas Capens <nicolascapens@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org>