back_gesture: Bump up splitview divider's resizable area.

Bump up the splitview divider's resizable area from 64dips to 96dips.

Bug: 1035126
Change-Id: If0cde6b8c95be47a0871780c8fe4fdd2972f24d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980960Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Min Chen <minch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727249}

ash/wm/toplevel_window_event_handler.cc

@@ -49,7 +49,7 @@ constexpr int kDragStartTopEdgeInset = 8;
 
 // Distance from the divider's center point that reserved for splitview
 // resizing in landscape orientation.
-constexpr int kDistanceForSplitViewResize = 32;
+constexpr int kDistanceForSplitViewResize = 49;
 
 // Returns whether |window| can be moved via a two finger drag given
 // the hittest results of the two fingers.