Android: Merge flags for overscroll history navigation

Extends the feature flag |kOverscrollHistoryNavigation| to be used for
Android platform as well, and remove the newly added one
|kGestureNavigation|.

Bug: 865567
Change-Id: I580120235825966b059190779e99e4957c436578
Reviewed-on: https://chromium-review.googlesource.com/c/1424628
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630674}
10 files changed