Redesign of "extract header list values" expected

[annevk]

Hi, I'm planning to change something you use, in whatwg/fetch#814. The new design should be relatively straightforward for you, provided implementations actually use the ABNF for their parsers.

It would be something like:

1. Let linkValues be the result of getting Link from identifierResponse's header list.
2. If linkValues is non-null, then:
   1. Let parsedLinkValues be the result of parsing linkValues per the #link-value ABNF. [RFC link]
   2. For each parsedLinkValue of parsedLinkValues:
      1. [Current processing of post-parsed-value goes here.]

Let me know if you have any concerns with this.