We use a ZoneVector because we do a fair amount of random access e.g.
in ExpressionClassifier::Accumulate() so the vector is better suited
than ZoneChunkList as it has constant time random access.

Bug: v8:6333
Change-Id: I83e1de60ee8fe319cfa5ce77fc5f5f86beb5307d
Reviewed-on: https://chromium-review.googlesource.com/1054672Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55315}