Adding fling-to-delete.

- Also fixing issue where the drop target icon changes color slower than the text.

Change-Id: I0bfa59da5d202016342f1c3de419ebcafd81ff6f

src/com/android/launcher2/DragSource.java

@@ -25,5 +25,6 @@ import com.android.launcher2.DropTarget.DragObject;
  *
  */
 public interface DragSource {
+    boolean supportsFlingToDelete();
     void onDropCompleted(View target, DragObject d, boolean success);
 }