Pass a top-level navigation initiator origin to Fetch

This helps with the HTTP WG's layered cookies draft integration work. whatwg/fetch#1807 depends on this state being passed in so we can define SameSite=Strict properly.

Author: bvandersloot-mozilla

source

@@ -2689,6 +2689,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
        <li><dfn data-x="concept-request-initiator-type" data-x-href="https://fetch.spec.whatwg.org/#request-initiator-type">initiator type</dfn></li>
        <li><dfn data-x="concept-request-service-workers-mode" data-x-href="https://fetch.spec.whatwg.org/#request-service-workers-mode">service-workers mode</dfn></li>
        <li><dfn data-x="concept-request-traversable-for-user-prompts" data-x-href="https://fetch.spec.whatwg.org/#concept-request-window">traversable for user prompts</dfn></li>
+       <li><dfn data-x-href="https://fetch.spec.whatwg.org/#request-top-level-navigation-initiator-origin">top-level navigation initiator origin</dfn></li>
        <li><dfn data-x-href="https://fetch.spec.whatwg.org/#concept-request-add-range-header">add a range header</dfn></li>
       </ul>
      </li>
@@ -104298,6 +104299,11 @@ location.href = '#foo';</code></pre>
     </dl>
    </li>
 
+   <li><p>If <var>navigable</var> is a <span>top-level traversable</span>, then set
+   <var>request</var>'s <span>top-level navigation initiator origin</span> to <var>entry</var>'s
+   <span data-x="she-document-state">document state</span>'s <span
+   data-x="document-state-initiator-origin">initiator origin</span>.</p></li>
+
    <li>
     <p>If <var>request</var>'s <span data-x="concept-request-client">client</span> is null:</p>