- Refactors most of the logic into a helper CanonicalizeShuffle
  overload that is more easily tested.
- Reorders these methods to be in the order they're used.
- Adds unit tests for this helper.

Bug: v8:6020
Change-Id: Ia7e08bd2ff3ae62b13c9283c6de04e0e1e85086b
Reviewed-on: https://chromium-review.googlesource.com/1118706Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54303}