message: Change 2 CHECK in BufferLiveness::live_range_strictly_before to DCHECK
  Executing VerifyBuffer can take up up to 6% of the total compile time for
  some model (25% of BufferAssignment) so making it debug only seems reasonable.
diff: @@ -94,8 +94,8 @@ string BufferLiveness::ToString() const {
  bool BufferLiveness::live_range_strictly_before(const LogicalBuffer& a,
  const LogicalBuffer& b) const {
  - TF_CHECK_OK(points_to_analysis_->VerifyBuffer(a));
  - TF_CHECK_OK(points_to_analysis_->VerifyBuffer(b));
  + TF_DCHECK_OK(points_to_analysis_->VerifyBuffer(a));
  + TF_DCHECK_OK(points_to_analysis_->VerifyBuffer(b));
  if (!hlo_ordering_->ExecutesBefore(a.instruction(), b.instruction())) {
  return false;
  