Fix COOP enforcement in redirects

Using the filtered response's header list in case of a redirect meant we wouldn't get access to the COOP header.

#8740 tracks the more general issue here.

Author: hemeryar

source

@@ -2578,6 +2578,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
        <li><dfn data-x="concept-response-timing-info" data-x-href="https://fetch.spec.whatwg.org/#concept-response-timing-info">timing info</dfn></li>
        <li><dfn data-x="concept-response-service-worker-timing-info" data-x-href="https://fetch.spec.whatwg.org/#response-service-worker-timing-info">service worker timing info</dfn></li>
        <li><dfn data-x="concept-response-has-cross-origin-redirects" data-x-href="https://fetch.spec.whatwg.org/#response-has-cross-origin-redirects">has-cross-origin-redirects</dfn></li>
+       <li><dfn data-x="concept-filtered-response-opaque-redirect" data-x-href="https://fetch.spec.whatwg.org/#concept-filtered-response-opaque-redirect">opaque-redirect filtered response</dfn></li>
        <li>
         <dfn data-x-href="https://wicg.github.io/background-fetch/#extract-content-range-values">extract content-range values</dfn>
         <!-- TODO: move this to FETCH -->
@@ -81704,9 +81705,10 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
    <li><p>If <var>reservedEnvironment</var> is a <span>non-secure context</span>, then return
    <var>policy</var>.</p></li>
 
-   <li><p>Let <var>value</var> be the result of <span>getting a structured field value</span> given
-   `<code>Cross-Origin-Opener-Policy</code>` and "<code data-x="">item</code>" from
-   <var>response</var>'s <span data-x="concept-response-header-list">header list</span>.</p></li>
+   <li><p>Let <var>parsedItem</var> be the result of <span>getting a structured field value</span>
+   given `<code>Cross-Origin-Opener-Policy</code>` and "<code data-x="">item</code>" from
+   <var>response</var>'s <span>unsafe response</span>'s <span
+   data-x="concept-response-header-list">header list</span>.</p>
 
    <li>
     <p>If <var>parsedItem</var> is not null, then:</p>
@@ -131643,6 +131645,7 @@ INSERT INTERFACES HERE
   Arne Thomassen,
   Aron Spohr,
   Arphen Lin,
+  Arthur Hemery,
   Arthur Sonzogni, <!-- ArthurSonzogni on GitHub -->
   Arthur Stolyar,
   Arun Patole,