Don't use a helper function to get the vertex attributes. The overhead of the function call ended up being a hot spot for draw calls since the attributes are iterated over many times in VertexDataManager. BUG=angleproject:959 Change-Id: I9bbfcbd115661ad629db9ed93d683cd8d0dc9a78 Reviewed-on: https://chromium-review.googlesource.com/263102 Tested-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>