We now don't absolutize the URL during parsing, keeping it as a CSS::URL
object which we then pass to the "fetch an external image for a
stylesheet" algorithm. Our version of this algorithm is a bit ad-hoc,
in order to make use of SharedResourceRequest. To try and reduce
duplication, I've pulled all of fetch_a_style_resource() into a static
function, apart from the "actually do the fetch" step.
See the spec issue in the comments for details. There are situations
where we will need to call this but don't have a CSSStyleSheet to pass
in, but we always have a Document, so use that where possible.
To prepare for introducing a CSS::URL type, we need to qualify any use
of LibURL as `::URL::foo` instead of `URL::foo` so the compiler doesn't
get confused.
Many of these uses will be replaced, but I don't want to mix this in
with what will likely already be a large change.
URL::basic_parse has a subtle bug where the resulting URL is not set
to valid when StateOveride is provided and the URL parser early returns
a valid URL.
This has not surfaced as a problem so far, as the only users of the
state override API provide an already valid URL buffer and also ignore
the result of basic parsing with a state override.
However, this bug surfaces implementing the URL pattern spec, which as
part of URL canonicalization:
* Provides a dummy URL record
* Basic URL parses that URL with state override
* Checks the result of the URL parser to validate the URL
While we could set URL validity on every early return of the URL parser
during state override, it has been a long standing FIXME around the code
to try and remove the awkward validity state of the URL class. So this
commit makes the first stage of this change by migrating the basic
parser API to return Optional, which also happens to make this subtle
issue not a problem any more.
