UserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.86 Safari/537.36

Steps to reproduce the problem:
1. create a dom
2. set dom.style to be "overflow-x :hidden; overflow-y:scroll;"
3. use getComputedStyle( dom ).overflow 

What is the expected behavior?
* In the earlier version it return "scroll"
* I test this case in Chrome v58, v58, MSIE9, FireFox v54, the new version of FireFox and Chrome return empty string

What went wrong?
what getComputedStyle should return in this case/

Did this work before? Yes Chrome/58.0.3029.110 

Chrome version: 59.0.3071.86  Channel: stable
OS Version: 10.0
Flash Version: 

following is the test code:
```javascript
(function(){
    function check( style, list ){
        var d  = document.createElement( 'div' ),
            id = d.id = 't-' +( +new Date );

        d.innerHTML = '<style>#' + id + ' div{' + style + '}</style><div/>';

        document.body.appendChild( d );
        var ii = list.length,
            s  = getComputedStyle( d.querySelector( 'div' ) );
        console.log( '' );
        console.log( 'style : ' + style );
        while( ii-- ){
            console.log( list[ ii ] + ' : ' + s[ list[ ii ] ] );
        }
        document.body.removeChild( d );
    }

    console.log( navigator.userAgent );

    check(
        'overflow-x :hidden; overflow-y:scroll;',
        'overflow,overflowX,overflowY'.split( ',' )
    );

    check(
        'overflow-x :visible; overflow-y:scroll;',
        'overflow,overflowX,overflowY'.split( ',' )
    );

    check(
        'overflow :hidden;',
        'overflow,overflowX,overflowY'.split( ',' )
    );

})();
```

Following is the result:
```
Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36

style : overflow-x :hidden; overflow-y:scroll;
overflowY : scroll
overflowX : hidden
overflow : scroll

style : overflow-x :visible; overflow-y:scroll;
overflowY : scroll
overflowX : auto
overflow : auto

style : overflow :hidden;
overflowY : hidden
overflowX : hidden
overflow : hidden

Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 10.0; WOW64; Trident/7.0; .NET4.0C; .NET4.0E; .NET CLR 2.0.50727; .NET CLR 3.0.30729; .NET CLR 3.5.30729)
style : overflow-x :hidden; overflow-y:scroll;
overflowY : scroll
overflowX : hidden
overflow : scroll
style : overflow-x :visible; overflow-y:scroll;
overflowY : scroll
overflowX : visible
overflow : scroll
style : overflow :hidden;
overflowY : hidden
overflowX : hidden
overflow : hidden

Mozilla/5.0 (Windows NT 10.0; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0 

style : overflow-x :hidden; overflow-y:scroll; 
overflowY : scroll 
overflowX : hidden 
overflow :  

style : overflow-x :visible; overflow-y:scroll; 
overflowY : scroll 
overflowX : auto 
overflow :  

style : overflow :hidden; 
overflowY : hidden 
overflowX : hidden 
overflow : hidden

Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.86 Safari/537.36

style : overflow-x :hidden; overflow-y:scroll;
overflowY : scroll
overflowX : hidden
overflow : 

style : overflow-x :visible; overflow-y:scroll;
overflowY : scroll
overflowX : auto
overflow : 

style : overflow :hidden;
overflowY : hidden
overflowX : hidden
overflow : hidden
```