We'd flatten upon compile anyway; and hashing the cons string also
creates a local flattened version that's not cached.

Change-Id: Ib5c82385ab009464b45bf1ceb289d04caaa77fcf
Reviewed-on: https://chromium-review.googlesource.com/c/1309827Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57182}