UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.75 Safari/537.36

Example URL:
https://jsfiddle.net/dnx7b8sm/1/

Steps to reproduce the problem:
1. Please see my attached JsFiddle. Just create any web component that uses a host-context/host combination, like, for example :host-context(.a):host(.c)

What is the expected behavior?
The CSS should be applied. 

What went wrong?
The CSS is ignored. It used to work in Chrome 49, but stopped working in Chrome 50.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? Yes Chrome 49

Does this work in other browsers? Yes 

Chrome version: 50.0.2661.75  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: Shockwave Flash 21.0 r0

This is a related bug: 

  https://bugs.chromium.org/p/chromium/issues/detail?id=604633

Also, maybe this is the problem: 
    https://codereview.chromium.org/1695393002 

 ..."Similarly, nothing left of :host or :host-context will ever match, so
we can treat those the same way. Selectors like "div + :host" or
":only-child:host-context(.a)" will never match. There is nothing in
the CSS Scoping spec which says they're invalid"...

Other changes that might be related:

   https://codereview.chromium.org/1703893002
   https://codereview.chromium.org/1683923003

The list of all changes is here:

   https://chromium.googlesource.com/chromium/src/+log/49.0.2623.112..50.0.2661.75?pretty=fuller&n=10000