Collecting some data on notification panel gestures.

Look for it in /sdcard/statusbar_gestures.dat, in "JSON
lines" format: one list of gestures per line; each gesture
is itself a list of objects representing motion events and
tags (annotations).

Exploded example:

  [ // list of gestures
    [ // this starts a gesture
      {"type":"motion",
       "time":1347697,  // in SystemClock.uptimeMillis() base,
                        // like MotionEvents
       "action":"down", // down, up, move, cancel, else numeric
       "x":277.61,
       "y":1.00
      },
      {"type":"tag",
       "time":1347701,
       "tag":"tracking", // "tracking" or "fling"
       "info":"collapsed" // extra stuff
      },
      ... // more events
    ],
    ... // more gestures
  ]
  // newline
  [ // another list of gestures
    ...
  ]
  ...

Change-Id: Ifacbf03749c879cd82fb899289fb79a4bdd4fc3b