A VertexFormat is similar to a simplified VertexAttribute, without
extra unncessary data. VertexFormats will be useful for GPU vertex
conversions with dynamic shader compilation.

Change-Id: I4e60e0a12d5f081fb52d95c8977c43d481b33bff
Reviewed-on: https://chromium-review.googlesource.com/184398Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>