Add a test for documents without browsing contexts loading stylesheets.

tests/wpt/web-platform-tests/html/semantics/document-metadata/the-link-element/stylesheet.py

@@ -0,0 +1,9 @@
+def main(request, response):
+    try:
+        count = int(request.server.stash.take(request.GET["id"]))
+    except:
+        count = 0
+    if "count" in request.GET:
+        return str(count)
+    request.server.stash.put(request.GET["id"], str(count + 1))
+    return 'body { color: red }'