GitLab

Adds a Toolbar Button that will be used to contract the toolbar/omnibox.
The contract button is only shown when the Toolbar is expanded. A simple animation is used.
Currently the button has no functionality, that will be added in a follow up CL.

Screenshot:
https://drive.google.com/open?id=1UIiS-Y1JTKwuU7lrQACtDK8RL1g10_7K

Bug: 790763
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Icf2d7e3b866c2f87f7346556f41328ba19044bfd
Reviewed-on: https://chromium-review.googlesource.com/802831
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521015}