The main change is the tab strip is a copy-paste of the old tab
strip, abandoning the previous implementation which attempted to move
things one-at-a-time. Things related to TabController were removed.
Most features (like dragging) that aren't currently supported are
commented out with a brief TODO so they can be added back later.

Separate out experimental tab painting from the tab class itself. There
is a lot of painting code and the tabs will get much more complicated,
so separating these will help code clarity.

Make the experimental tab controller work on non-Windows Views builds.

Updates to the model and tab to work better.

Bug: 
Change-Id: Iec432dc3ca1ccf18cc240656fa5e81f3c9fe51a4
Reviewed-on: https://chromium-review.googlesource.com/765212


Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516042}