Add multiple header fields support for the Link header parser

Add multiple header fields support for the Link header parser

This CL adds support for concatenated Link header fields (so multiple fields, separated by a comma). It does so by adding a LinkHeaderSet class, that drives the parsing process and contains LinkHeader objects.

BUG=456076
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=189648

[Yoav Weiss, 2015-02-06 13:42:25]

yoav@yoav.ws changed reviewers:
+ mkwst@chromium.org

[Mike West, 2015-02-06 13:54:13]

This is a reasonable approach. LGTM.

For comparison, CSP splits the whole string on ',', which simplifies some of the
processing (see
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...).
I don't think it's worth rewriting all this to go that route, however.

[Yoav Weiss, 2015-02-06 14:00:14]

On 2015/02/06 13:54:13, Mike West wrote:
> This is a reasonable approach. LGTM.
> 
> For comparison, CSP splits the whole string on ',', which simplifies some of
the
> processing (see
>
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...).
> I don't think it's worth rewriting all this to go that route, however.

I thought of going that route, but my childhood traumas with srcset parsing and
data URIs (which contain commas) caused me to prefer this route :)

[Mike West, 2015-02-06 14:05:36]

On 2015/02/06 at 14:00:14, yoav wrote:
> On 2015/02/06 13:54:13, Mike West wrote:
> > This is a reasonable approach. LGTM.
> > 
> > For comparison, CSP splits the whole string on ',', which simplifies some of
the
> > processing (see
> >
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...).
> > I don't think it's worth rewriting all this to go that route, however.
> 
> I thought of going that route, but my childhood traumas with srcset parsing
and data URIs (which contain commas) caused me to prefer this route :)

Note that it's impossible to distinguish between a server that returns:

  Link: header with a comma right here -->,<--

from a server that returns:

  Link: header with a comma right here -->
  Link: <--

The network stack concatenates them with a comma, and there's not much you can
do about it. So commas inside URLs need to be escaped... that's how CSP deals
with things, in any event.

Regardless, this is fine. :)

[Yoav Weiss, 2015-02-06 14:06:40]

The CQ bit was checked by yoav@yoav.ws

[commit-bot: I haz the power, 2015-02-06 14:07:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/907453002/1

[commit-bot: I haz the power, 2015-02-06 14:59:09]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=189648