Key message we could find in the source code:
1. after sap.ca.ui.utils.busydialog.requireBusyDialog() is called in application, we can only see the rotating wheel in UI after 1.5 seconds - defined in BUSYDIALOG_TIMEOUT.
2. the requireBusyDialog and releaseBusyDialog must be called in pair. There is private variable _iRequiredCount maintained inside the implementation. When require function is called, _iRequiredCount++; release for _iRequiredCount--.
3. it is obsolete. New application should use sap.m.BusyDialog instead.
test2：将timeout从默认的1500ms改成30000ms:
sap.ca.ui.utils.BUSYDIALOG_TIMEOUT = 30000;
第一个video timeout_1500.wmv: 虽然list和detail的数据都ready了，但是因为ETAG需要10s才能返回，整个UI被这个ETAG的request造成的busy dialog锁住了，直到10s后UI才能点击
第二个video是把默认的timeout从1500毫秒改成30秒，即busy dialog不会显示。从video里看出UI始终是可操作的，尽管后台的ETAG还没有回来。
