Fix 3377113: Mini homescreen outline wrong color

Couldn't repro this reliably, but the only way I could see
it happening is if we got an UP event without a MOVE at the
same location. This patch prevents that from happening.

Change-Id: I473c4ea50474b45da8c5537efe39177c1423ae20

src/com/android/launcher2/DragScroller.java

@@ -26,6 +26,7 @@ public interface DragScroller {
 
     /**
      * The touch point has entered the scroll area; a scroll is imminent.
+     * This event will only occur while a drag is active.
      *
      * @param direction The scroll direction
      */
@@ -33,6 +34,7 @@ public interface DragScroller {
 
     /**
      * The touch point has left the scroll area.
+     * NOTE: This may not be called, if a drop occurs inside the scroll area.
      */
     void onExitScrollArea();
 }