Remove linked_ptr from content/.

BUG=556939

Change-Id: I8e5950ade205d557c2132b478863a1c0a8935eff
Reviewed-on: https://chromium-review.googlesource.com/c/1358644
Reviewed-by: Leonard Grey <lgrey@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613588}
4 files changed