Monotonicity is not required at the current setup, where we do backward pass through
the graph.  However, for bidirectinal analysis, we'd better be sure that all the
input/use information is monotone.

The checker here is quite strict - it requires monotonicity in each of: use
representations, use truncation, output representation and output type. In future, we can
lower the requirements and use lexicographic ordering (e.g., on use truncation and
representation).

Review URL: https://codereview.chromium.org/1473733007

Cr-Commit-Position: refs/heads/master@{#32392}