Window flicker when drag in the original titlebar area and move to top of the screen

[xiaodw]

This problem reproduce with the latest code. And some app such as SoureTree\WeChat has the problem also,reason and solution as below:
The problem caused by the call of convertBaseToScreen(INAppStoreWindow.m line 567),it works well if caculate the offset of window move without the convert.
NSPoint now = [window convertBaseToScreen:theEvent.locationInWindow];
NSPoint now = [NSEvent mouseLocation];