Create test for factor value of ScaleGesture.

A ScaleGestureDectector is attached to an activity.

A pinch and zoom action has been created, and mimics the action by first
sending a down motion on the two points,
which then moves to the supplied end coordinates in the number of steps
(PINCH_STEP_COUNT).

Bug: 30751698
Change-Id: Id654025f47dfc10d852e9f2eb428a969fc7de95c