UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.108 Safari/537.36

Example URL:
N/A

Steps to reproduce the problem:
1. start Chrome with fresh user-data-dir and proxy-pac-url and direct it to http URL. Sample command-line arguments:
["--user-data-dir=/private/var/folders/_h/dcx4zqvn7qz8rhxb0wj_zw89_1nlml/T/jsh7331110360449534818.tmp/","--proxy-pac-url=http://127.0.0.1:58587/proxy.pac","http://foo/"]

chrome://net-internals#proxy shows:
Effective proxy settings
PAC script: http://127.0.0.1:58587/proxy.pac

Contents of PAC file at http://127.0.0.1:58587/proxy.pac:
function FindProxyForURL(url, host) {
	if (host == "foo") return "PROXY 127.0.0.1:58585";
	return "DIRECT";
}

What is the expected behavior?
The page at http://127.0.0.1:58585/ should be returned.

What went wrong?
1. If http:// URL is specified on command line, or typed into address bar, the browser force-redirects to https:// URL (nothing is shown for this in the DevTools Network tab).

2. The connection then fails with "ERR_TUNNEL_CONNECTION_FAILED"

Did this work before? Yes Unsure, but breakage is very recent, probably worked in Chrome 62

Chrome version: 63.0.3239.108  Channel: stable
OS Version: OS X 10.12.6
Flash Version: 

Also fails on Linux; other operating systems untested