Replaces the anchor page circular doubly linked list
with a doubly linked list pointing to nullptr on its ends.

Fixes a memory leak when rewinding pages.

The large pages list will move to the new list implementation
in a follow-up CL.

Change-Id: I2933a5e222d4ca768f4b555c47ed0d7a7027aa73
Reviewed-on: https://chromium-review.googlesource.com/1060973
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53288}