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If the app list is not opened and shelf is visible, swipe up on the shelf
should show the app list.
If the app list is opened, swipe up on the shelf should keep the app list
opened. Tap anywhere else of shelf should close the app list.

This is the basic one currently. Will add some simple animations followed.
(e.g, change the opacity of the searchbox and apps row by row according
to the dragging amount)

Bug: 735999,742461
Change-Id: I5eb8b6d4d006a50720050b34168849e9d57370f2
Reviewed-on: https://chromium-review.googlesource.com/562739
Commit-Queue: min c <minch@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488781}