[ios] Create some initial files for new tab grid.

This CL creates stub files for the new tab grid's coordinator and
view controller.

Bug: 804496
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I68cc168e7c7d1d3329e4cbfb3eb03a47c9d62c9a
Reviewed-on: https://chromium-review.googlesource.com/914609
Commit-Queue: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536366}
7 files changed