Unexpected "Cannot parse URL: relative URL with a cannot-be-a-base base" in two WPT tests

[pshaughn]

In html/browsers/browsing-the-web/navigating-across-documents/005/html, .click() is called on an anchor with href="href.html".
In html/browsers/browsing-the-web/navigating-across-documents/source/navigate-child-function-parent.html, an iframe's contentWindow.location is assigned "support/dummy/html".
In both cases we end up with "Cannot parse URL: relative URL with a cannot-be-a-base base". This message is probably coming from the url crate; either we're passing garbage in as the base URL, or (probably less likely) the url crate's broken.

[jdm]

I suspect the documents are about:blank documents, which is not a valid base URL.

[pshaughn]

In 005.html the anchor being clicked is on the main 005.html page itself; an iframe is present as the target of the anchor, however, so it could be the URL is being computed relative to that instead of the main page.