[iOS] Use ToolbarContainerCoordinator for secondary toolbar.

This CL adds code to use a ToolbarContainerCoordinator to manage the
layout of the secondary toolbar.  This moves some fullscreen logic from
BVC and into the toolbar container view controller.  The added code is
behind the kToolbarContainerEnabled flag.

Bug: 880672
Cq-Include-Trybots: luci.chromium.try:ios-simulator-cronet;luci.chromium.try:ios-simulator-full-configs
Change-Id: Icd2e3b48bb0947b871bd4855a83a78c1a58af0e4
Reviewed-on: https://chromium-review.googlesource.com/c/1222915
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600251}
9 files changed