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- Add the thumb strip coordinator to the browser coordinator.
- Add a reference to the thumb strip pan handler inside the BVC so that
the BVC can add the tab strip and the toolbar as animatees of the view
revealing vertical pan handler.
- Implement the view revealing animatee protocol: when revealing the
view, the tab strip should be translated down to be hidden behind
the toolbar.
- Set the BVC's background colour to clear and remove the fake status
bar so that the thumb strip can be visible from behind those.
- Add a pan gesture recognizer to the toolbar and tab strip, the first
set of entry points to the thumb strip.
- Set the tab strip to be below the toolbar in the view hierarchy so that
it can slide behind the toolbar during thumb strip transitions.

Bug: 1094335
Change-Id: Ic749236f70f5c3a589ae70e5b6a9442e85acf517
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315029
Commit-Queue: Roberto Moura <mouraroberto@google.com>
Auto-Submit: Roberto Moura <mouraroberto@google.com>
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803160}