Get rid of yet another ZoneChunkList.

Change-Id: If63b1b87e007f4d146532b2c66f101280d3fcf2f
Reviewed-on: https://chromium-review.googlesource.com/c/1421319Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59027}