Adding debugging for last active time.

        Recents.getTaskLoader().dump(prefix, writer);

        String id = Integer.toHexString(System.identityHashCode(this));

        long lastStackActiveTime = Prefs.getLong(this,

                Prefs.Key.OVERVIEW_LAST_STACK_TASK_ACTIVE_TIME, -1);

        writer.print(prefix); writer.print(TAG);

        writer.print(" visible="); writer.print(mIsVisible ? "Y" : "N");

        writer.print(" lastStackTaskActiveTime="); writer.print(lastStackActiveTime);

        writer.print(" currentTime="); writer.print(System.currentTimeMillis());

        writer.print(" [0x"); writer.print(id); writer.print("]");

        writer.println();