URLSearchParams returns null on Get for value that is present

[gterzian]

Used in

servo/tests/wpt/web-platform-tests/html/browsers/browsing-the-web/history-traversal/persisted-user-state-restoration/resources/post_name_on_load.html

Line 5 in 07ba57b

window.opener.postMessage(params.get('name'), '*');

where window.location.search is ?name=foo, but params.get('name') return null.

which currently makes the below test time out.

https://github.com/servo/servo/blob/master/tests/wpt/web-platform-tests/html/browsers/browsing-the-web/history-traversal/persisted-user-state-restoration/resume-timer-on-history-back.html

code:

servo/components/script/dom/urlsearchparams.rs

Line 88 in 07ba57b

fn Get(&self, name: USVString) -> Option<USVString> {

spec: https://url.spec.whatwg.org/#dom-urlsearchparams-get