Correct unload event timing for different COOP

Sometimes a navigation causes a BCG swap, e.g. when the cross-origin isolated capability changes. In that case:

* The timestamps should coarsened based on both documents.
* Some user-agents unload in parallel, which should not become part of the new document's timing info.
* Time origin should be according to the new global's time origin, but coarsened by both.

Closes w3c/navigation-timing#169.

source

@@ -90144,7 +90144,8 @@ new PaymentRequest(…); // Allowed to use
 
    <li>
     <p><span data-x="unload a document">Unload</span> <var>previousDocument</var> with
-    <var>unloadTimingInfo</var>.</p>
+    <var>unloadTimingInfo</var> and <var>newDocument</var>'s
+    <span>relevant global object</span>.</p>
 
     <p>If this instance of the <span data-x="navigate">navigation</span> algorithm is canceled while
     this step is running the <span>unload a document</span> algorithm, then the <span>unload a
@@ -90154,6 +90155,11 @@ new PaymentRequest(&hellip;); // Allowed to use
     execution occurring as part of unloading the document or its descendants.)</p>
    </li>
 
+   <li><p>If <var>newDocument</var>'s <span>event loop</span> is not <var>previousDocument</var>'s
+   <span>event loop</span>, then the user agent may <span data-x="unload a document">unload</span>
+   <var>previousDocument</var> <span>in parallel</span>, In that case, the user agent should set
+   <var>unloadTimingInfo</var> to null.</p></li>
+
    <li><p>If <var>navigationParams</var>'s <span
    data-x="navigation-params-has-cross-origin-redirects">has cross-origin redirects</span> is false,
    and <var>newDocument</var>'s <span data-x="concept-document-origin">origin</span> is the <span
@@ -91429,8 +91435,9 @@ dictionary <dfn dictionary>PageTransitionEventInit</dfn> : <span>EventInit</span
   </ol>
 
   <p>To <dfn export data-x="unload a document" data-lt="unload a document">unload</dfn> a
-  <code>Document</code> <var>document</var>, given an optional <var>recursiveFlag</var> and a
-  <span>document unload timing info</span>-or-null <var>unloadTimingInfo</var> (default null):</p>
+  <code>Document</code> <var>document</var>, given an optional <var>recursiveFlag</var>, a
+  <span>document unload timing info</span>-or-null <var>unloadTimingInfo</var> (default null),
+  and an optional <span>global object</span> <var>newGlobal</var>:</p>
 
   <ol>
    <li><p>Increase the <span>event loop</span>'s <span>termination nesting level</span> by
@@ -91457,11 +91464,14 @@ dictionary <dfn dictionary>PageTransitionEventInit</dfn> : <span>EventInit</span
      <li><p><span>Update the visibility state</span> of <var>newDocument</var> to
      "<code data-x="">hidden</code>".</p></li>
     </ol>
-  </li>
+   </li>
 
    <li><p>If <var>unloadTimingInfo</var> is not null, then set <var>unloadTimingInfo</var>'s
    <span>unload event start time</span> to the <span>current high resolution time</span> given
-   <var>document</var>'s <span>relevant global object</span>.</p></li>
+   <var>newGlobal</var>, <span data-x="coarsen time">coarsened</span> given <var>document</var>'s
+   <span>relevant settings object</span>'s <span
+   data-x="concept-settings-object-cross-origin-isolated-capability">cross-origin isolated
+   capability</span>.</p></li>
 
    <li><p>If <var>document</var>'s <i data-x="concept-document-salvageable">salvageable</i> state is
    false, then <span data-x="concept-event-fire">fire an event</span> named
@@ -91470,7 +91480,10 @@ dictionary <dfn dictionary>PageTransitionEventInit</dfn> : <span>EventInit</span
 
    <li><p>If <var>unloadTimingInfo</var> is not null, then set <var>unloadTimingInfo</var>'s
    <span>unload event end time</span> to the <span>current high resolution time</span> given
-   <var>document</var>'s <span>relevant global object</span>.</p></li>
+   <var>newGlobal</var>, <span data-x="coarsen time">coarsened</span> given <var>document</var>'s
+   <span>relevant settings object</span>'s <span
+   data-x="concept-settings-object-cross-origin-isolated-capability">cross-origin isolated
+   capability</span>.</p></li>
 
    <li><p>Decrease the <span>event loop</span>'s <span>termination nesting level</span> by
    one.</p></li>