Remove linked_ptr from extensions declarative web requests.

BUG=582001

Change-Id: I15b7783fa2a409e25ed9764a0b274e403db5808b
Reviewed-on: https://chromium-review.googlesource.com/c/1368688
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618596}
11 files changed