Fix URL parsing for URL with no protocol

Seems connect-assets could not handle //cdn.example.com/assets/ path
it has to explicitly be http://cdn.example.com/assets to be parsed
by url.parse, this may not work for pages that can be served both
by http and https.

url.parse has a slashesDenoteHost flag to allow parsing of //cdn.example.com

Change-Id: Ibb52cd148e1c646763ebc6afce587e9f89aebcd2