Auto merge of #10247 - eddyb:document-base-url, r=<try>

Use <base> in resolving url attributes (like "href").

Second take of #6303, now that the `base_url` infrastructure is in place.

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components/script/dom/element.rs

@@ -1078,7 +1078,7 @@ impl Element {
         }
         let url = self.get_string_attribute(local_name);
         let doc = document_from_node(self);
-        let base = doc.url();
+        let base = doc.base_url();
         // https://html.spec.whatwg.org/multipage/#reflect
         // XXXManishearth this doesn't handle `javascript:` urls properly
         match base.join(&url) {