UserAgent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0

Steps to reproduce the problem:
The problem has been detailed here: https://github.com/nwjs/nw.js/issues/6201

Steps are as follows

With a basic template containing a simple HTML page and the window set to frameless, open the developer tools and set the css attribute -webkit-app-region: drag for the html or body element.
Try to drag the window by dragging the body element on that page and it will not drag.
Resize the app window and try dragging again, the page will now drag.
Unset/remove that property and drag the window again, it keeps dragging when it shouldn't since the property is no longer enabled.
Resize the app window and try dragging again, the page will now no longer drag.

What is the expected behavior?
When setting or unsetting the -webkit-app-region: drag on an element the app should be draggable when dragging that element or stop dragging when the property is unset.

What went wrong?
The property change only takes effect when there is a full page repaint. (i.e. font-family change, window resize, etc.)

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 63  Channel: n/a
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: 

This issue was requested by NWJS developer and can be read in more detail here: https://github.com/nwjs/nw.js/issues/6201