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Enables WebKit based side swipe, and only enables Chrome side swipe when the
page swiped page is to or from an NTP.

Change-Id: I892f7074252ee04b2d0b337ebd744f3ba9388e27
Reviewed-on: https://chromium-review.googlesource.com/c/1350192
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612042}