This will fire if the CAST is never useful. This is helpful if you add
a TNode return type to a function - its callers no longer need to cast
the result if the types are the same.

Change-Id: If0b04c615cb2dbfa91ba43d5d0d35ace5a31d4e7
Reviewed-on: https://chromium-review.googlesource.com/934449Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51599}