Previously we supplied individual parameters to the various drag and pan
callbacks. However, that approach isn't extensible because each new
parameter is a breaking change to the API.
This patch makes a one-time breaking change to the API to provide a
"details" object that we can extend over time as we need to expose more
information. The first planned extension is adding enough information to
accurately produce an overscroll glow on Android.
2d4acb8041