UserAgent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36

Steps to reproduce the problem:
This is reproducible by having a font-weight property (or another property that changes glyph width) applied to the ::first-line pseudo-element inside a flexible box context.  Please see my attachment or visit this JSFiddle: https://jsfiddle.net/Kredit/2bqnLnwb/

What is the expected behavior?
I expect all the text to be bold and on the same line, because there is no visible reason why the text should be wrapping on the last word.

Internet Explorer and Firefox both behave as expected, with all text bolded and on the same line with the browser window fully maximized.

What went wrong?
As long as there is more than 1 word in the inner .first-line div, it will be split onto a second line and thus not bolded.  Even having "One Two" as the inner text results in a line break being inserted between the words.

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 55.0.2883.87  Channel: n/a
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: Shockwave Flash 24.0 r0

Maybe this is being caused by the layout engine calculating how wide the flexbox should be before applying the ::first-line styles.  font-weight makes the text wider, meaning it would no longer fit inside the original size.