[iOS] Create ObjC container for fullscreen disabler observers.

This allows the proper memory management of ObserverLists used in
Objective-C blocks.

Bug: 816342
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ic3b232303586ec99129ab999740454a0180833bb
Reviewed-on: https://chromium-review.googlesource.com/939101
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#539541}(cherry picked from commit 212b7610b1f563d5753d5ad9c4b55c4cf637d514)
Reviewed-on: https://chromium-review.googlesource.com/942241
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#632}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
2 files changed