Pulling down on most kinds of apps can cause a split to be created without horizontal motion (when the touch originates within the split indicator widths). It is particularly easy for Chrome browser windows, where a small flick can start a split, without the indicators ever becoming visible. For ARC and other windows the app has to be dragged far enough for the indicators to appear for the split to happen.

To mitigate the possible unintended splits that could result from this kind of gesture, we should add two protections:
1) Splits should not occur until the split indicators have faded in
2) Touches near and in the split regions should follow the minimum horizontal drag thresholds established in crbug.com/843779