Window closing operation is not completed asynchronous execution

Mobile terminal, acquires not cache data cacheplug.getItem, the cache is not actually do the WEB SQL;

May be due to close the window after synchronization task is completed, this time asynchronous: cacheplug.setItem（异步存储，多次调用）not fully completed execution; therefore missing data;

Add a counter before each setItem +1; successful callback function invoked -1; 0 callback determines close the window;