[iOS] Continue broadcasting while new tab animations are occurring.

This allows BVC to intercept the animated fullscreen disabling action
for new foreground tabs.

Bug: 809120
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I8b3e4865a98cde6eeb36cd8fbd6d1ec05983d5ce
Reviewed-on: https://chromium-review.googlesource.com/935442
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#539244}(cherry picked from commit 6b2fe9dbe26a606b6c41e9efba9ba37f8e628f1b)
Reviewed-on: https://chromium-review.googlesource.com/941555
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#631}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
1 file changed