UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.59 Safari/537.36

Steps to reproduce the problem:
1. Include eg <link rel=preload as=document href=http://example.com> in HTML document
2. Console error: 'as' attribute rejected as not valid 

What is the expected behavior?
Expect http://example.com to be preloaded as per <link rel=preload as=document href=http://example.com> statement

What went wrong?
No preloading and console error: <link rel=preload> must have a valid `as` value

Did this work before? No 

Chrome version: 54.0.2840.59  Channel: stable
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: Shockwave Flash 23.0 r0

See 'document' example within official spec: https://w3c.github.io/preload/#developer-server-and-proxy-initiated-fetching