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This CL fixes the animation occuring when opening a new tab in
background when the flag to enable BrowserContainer fullscreen.

Bug: 836730
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ifa1abee606888938fe3b551903e16f92c7c60698
Reviewed-on: https://chromium-review.googlesource.com/1032772Reviewed-by: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557145}