This bug tracks basic tab switching functionality targeting fishfood. 
 crbug.com/641487 tracks the dogfood-grade complete tab feature.

For this bug, we should complete:

- UI API plumbing to feed the current tab state (name, id, site/favicon) to the HTML UI.
- UI API plumbing to let the UI switch tabs (based on the ID passed previously)
- A basic (ie. unpolished) UI to allow users to actually see and switch tabs
- If trivial, some visual indicator of which tabs are incognito

The feature-level tabs bug covers:

- Thumbnail images of tabs
- Scrolling panels of tabs
- Full incognito UI (darker theme, etc)
- New tab page
- Launching a new tab
(etc)

Filed related bug for fast-path gesture: https://bugs.chromium.org/p/chromium/issues/detail?id=691871

Specs forthcoming. Briefly:

* Tabs should live in their own subsection.
* This section should be accessible via button in menu w/ current tab count (ala Clank UI)
* They should be directly accessible via fast-path gesture, per bug 691871.
* They should be horizontally scrollable.
* UI tabs should split open tabs into "Open" and "Incognito" buckets. Phrasing for "Open" may change. This is under some discussion in broader Chrome UX team, I believe.

Updated mockups here: 

https://docs.google.com/document/d/139CuKm9NmArYqPAHIj5gXciGibUulcvyZvNKmVKjlwk/edit#