Implement button to get application info for an app shortcut.

For now, it's just a drag target like the delete zone. Once all apps
and the home screen support a selection mode, this (and delete) will
be implemented as buttons in the Contextual Action Bar.

Change-Id: I6bf43d03eefda672ea34c583a7021137da22b184

src/com/android/launcher2/DropTarget.java

@@ -72,8 +72,7 @@ public interface DropTarget {
 
     /**
      * Check if a drop action can occur at, or near, the requested location.
-     * This may be called repeatedly during a drag, so any calls should return
-     * quickly.
+     * This will be called just before onDrop.
      * 
      * @param source DragSource where the drag started
      * @param x X coordinate of the drop location