UserInputHandler cleanup.

Obtain DocumentDetails directly from Event...fixing stack trace.
Don't try to do stuff in UserIntputHandler on events w/o details.
Don't call TouchDelegate#onLongPress for mouse events.
Don't clear selection when clicking in mime type icon (w/o CTRL).

Bug: 31350922,31381545

Change-Id: Ibc4e5335cdb41569f9863d87f82dafca58659974