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Removes all Tab dependencies on displaying the SadTab View.
This is done by creating a SadTabLegacyCoordinator that
encapsulates the SadTabView presentation. This coordinator is owned
and created by BrowserViewController. 

Bug: 
Change-Id: Ic263f26af1ea81a293c05f0944d97e996ff7a6b2
Reviewed-on: https://chromium-review.googlesource.com/651756
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500000}