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This CL change the reverse scroll gestures including

 - Swipe up with three fingers to enter overview and down to exit
 overview. In M87, the old gestures also work and a notification shows
 up. In M88, the old gestures fail. In M89, remove notification.

 -For each user, the notification will only show 3 times

 - Swipe right to switch to the next desk and left to switch to the
 previous desk. The old gestures fail immediately.

Bug: 1107183

Change-Id: I815c308c1fee4cf5152227064c5f8fec61f67b06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2418015
Commit-Queue: Xiaodan Zhu <zxdan@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809375}