Dragging in touch explore mode should not become exploring.

In touch exploration two fingers in the same direction drag and if one of them
goes up the other starts to touch explore. This however causes inadvertent touch
exploring to happen on almost every scroll causing confusion. Now two finger
drag and they should both go up to allow exploring. This way the inadvertent
exploring is gone and user experience is much better.

bug:5440411

Change-Id: Id8aaece92e5dea1fc740400d2adc9dd63a1674e4