This simplifies the ExpressionClassifier a bit again, making it a little more
understandable.

Change-Id: I57bdd871b10409ea04b33748609160f2b40a498a
Reviewed-on: https://chromium-review.googlesource.com/c/1348431Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57753}