kPagingTouchSlop top-level constant
The distance a touch has to travel for the framework to be confident that the gesture is a paging gesture. (Currently not used, because paging uses a regular drag gesture, which uses kTouchSlop.)
Implementation
// TODO(ianh): Create variants of HorizontalDragGestureRecognizer et al for
// paging, which use this constant.
const double kPagingTouchSlop = kTouchSlop * 2.0;