The test says that it is testing dictionary mode, but it is only
creating fast mode arrays.

Bug: chromium:852420
Change-Id: I99ccc997aaa87ecf49bddf02e46b7e543f535374
Reviewed-on: https://chromium-review.googlesource.com/c/1462918Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59504}