Fix NPE / add downX,Y location for all swipes/ add extra debugging info

Bug: 122700646
Bug: 127840207

Change-Id: I5862c8950565df172a933114e1fb2f9c4575593e

src/com/android/launcher3/touch/SwipeDetector.java

@@ -180,6 +180,13 @@ public class SwipeDetector {
         return mState == ScrollState.DRAGGING || mState == ScrollState.SETTLING;
     }
 
+    public int getDownX() {
+        return (int) mDownPos.x;
+    }
+
+    public int getDownY() {
+        return (int) mDownPos.y;
+    }
     /**
      * There's no touch and there's no animation.
      */