Update declarative web request classes.

This switches them to use Optional, and makes them
clonable in preparation for linked_ptr removal.

BUG=582001

Change-Id: I1ba6bb559b6fec703f41ad22ad670799ec61c91d
Reviewed-on: https://chromium-review.googlesource.com/c/1380819
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618368}
7 files changed