//
// For example suppose foo[...,3:, 2] on foo.shape=(2,2,3,4) then
// we need to produce the missing begin_mask, end_mask for the first two
// dimensions i.e. foo[:, :, 3:, 2].
static void BuildDenseSliceSpec(const SparseSliceSpec &sparse,
                                DenseSliceSpec *dense) {
  // Build expanded dense begin, end, strides, begin_mask, end_mask, and
  // shrink_axis_mask.