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This adds the complete MVC structure for a generic horizontal list of
chip views for filter selection.  This will be first used by the new
Download Home UI.

BUG=839489

Screenshot of widget placed in UI: https://drive.google.com/open?id=1Em7em1jg-GnEdyoGLwHUezfgryuJ-cja

Change-Id: I6a7f8a29280c5aeaf01c7be86c15f3fb64ba0288
Reviewed-on: https://chromium-review.googlesource.com/1042813Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#559224}