Fix object providence in event loops

Closes #4337, by being much clearer about how browsing contexts,
Documents, and Windows documents are selected for each turn of the event
loop processing model.

This also fixes an issue where the "report the duration of the update
the rendering step" referenced the out-of-scope variable "docs".

Author: domenic

source

@@ -89211,6 +89211,8 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
 
    <li><p><i>Microtasks</i>: <span>Perform a microtask checkpoint</span>.</p></li>
 
+   <li><p>Let <var>hasARenderingOpportunity</var> be false.</p></li>
+
    <li><p>Let <var>now</var> be the <span>current high resolution time</span>. <ref
    spec=HRT></p></li>
 
@@ -89238,9 +89240,9 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
 
     <ol>
      <li>
-      <p>Let <var>docs</var> be the list of <code>Document</code> objects associated with the
-      <span>event loop</span> in question, sorted arbitrarily except that the following conditions
-      must be met:</p>
+      <p>Let <var>docs</var> be all <code>Document</code> objects whose <span>relevant
+      agent</span>'s <span>event loop</span> is this event loop, sorted arbitrarily except that the
+      following conditions must be met:</p>
 
       <ul>
        <li><p>Any <code>Document</code> <var>B</var> whose <span
@@ -89262,11 +89264,9 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
      </li>
 
      <li>
-      <p><i>Rendering opportunites</i>: If there are <span data-x="browsing context">browsing
-      contexts</span> <var>browsingContexts</var> that do not have a <span>rendering
-      opportunity</span>, then remove from <var>docs</var> all <code>Document</code> objects whose
-      <span data-x="concept-document-bc">browsing context</span> is in
-      <var>browsingContexts</var>.</p>
+      <p><i>Rendering opportunities</i>: Remove from <var>docs</var> all <code>Document</code>
+      objects whose <span data-x="concept-document-bc">browsing context</span> do not have a
+      <span>rendering opportunity</span>.</p>
 
       <p>A <span>browsing context</span> has a <dfn>rendering opportunity</dfn> if the user agent is
       currently able to present the contents of the <span>browsing context</span> to the user,
@@ -89288,19 +89288,23 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
       a much slower 4 rendering opportunities per second, or even less.</p>
      </li>
 
-     <li><p><i>Unnecessary rendering</i>: If there are <span data-x="browsing context">browsing
-     contexts</span> <var>browsingContexts</var> for which the user agent believes updating the
-     rendering would have no visible effect and which possess no <code>Document</code> objects with
-     a non-empty <span>map of animation frame callbacks</span>, then remove from <var>docs</var>
-     all <code>Document</code> objects whose <span data-x="concept-document-bc">browsing
-     context</span> is in <var>browsingContexts</var>.</p></li>
+     <li><p>If <var>docs</var> is not empty, then set <var>hasARenderingOpportunity</var> to
+     true.</p></li>
 
      <li>
-      <p>If there are <span data-x="browsing context">browsing contexts</span>
-      <var>browsingContexts</var> for which the user agent believes it's preferrable to skip
-      updating the rendering for other reasons, then remove from <var>docs</var> all
-      <code>Document</code> objects whose <span data-x="concept-document-bc">browsing context</span>
-      is in <var>browsingContexts</var>.</p>
+      <p><i>Unnecessary rendering</i>: Remove from <var>docs</var> all <code>Document</code> objects
+      which meet both of the following conditions:</p>
+
+      <ul class="brief">
+       <li>The user agent believes that updating the rendering of the <code>Document</code>'s <span
+       data-x="concept-document-bc">browsing context</span> would have no visible effect, and</li>
+       <li>The <code>Document</code>'s <span>map of animation frame callbacks</span> is empty.</li>
+      </ul>
+     </li>
+
+     <li>
+      <p>Remove from <var>docs</var> all <code>Document</code> objects for which the user agent
+      believes that it's preferrable to skip updating the rendering for other reasons.</p>
 
       <div class="note">
        <p>The step labeled <i>Rendering opportunities</i> prevents the user agent from updating the
@@ -89359,6 +89363,25 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
      <li><p>For each <span>fully active</span> <code>Document</code> in <var>docs</var>, update the
      rendering or user interface of that <code>Document</code> and its <span
      data-x="concept-document-bc">browsing context</span> to reflect the current state.</p></li>
+
+     <li>
+      <p>Report the duration of the <span>update the rendering</span> step by performing the
+      following steps:</p>
+
+      <ol>
+       <li><p>Let <var>rendering end time</var> be the <span>current high resolution
+       time</span>.</p></li>
+
+       <li><p>Let <var>top-level browsing contexts</var> be the set of all <span data-x="top-level
+       browsing context">top-level browsing contexts</span> of the <span
+       data-x="concept-document-bc">browsing contexts</span> of all <span>fully active</span>
+       <code>Document</code>s in <var>docs</var>.</p></li>
+
+       <li><p><span>Report long tasks</span>, passing in <var>now</var> (repurposed as meaning the
+       beginning of the <span>update the rendering</span> step), <var>rendering end time</var>, and
+       <var>top-level browsing contexts</var>.</p></li>
+      </ol>
+     </li>
     </ol>
    </li>
 
@@ -89367,36 +89390,17 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
 
     <ul class="brief">
      <li>this is a <span>window event loop</span></li>
-     <li>there is no <span data-x="concept-task">task</span> in the <span>event loop</span>'s
+     <li>there is no <span data-x="concept-task">task</span> in this <span>event loop</span>'s
      <span data-x="task queue">task queues</span> whose <span
      data-x="concept-task-document">document</span> is <span>fully active</span></li>
-     <li>the <span>event loop</span>'s <span>microtask queue</span> is <span data-x="list is
+     <li>this <span>event loop</span>'s <span>microtask queue</span> is <span data-x="list is
      empty">empty</span></li>
-     <li>none of the <span data-x="browsing context">browsing contexts</span> have a
-     <span>rendering opportunity</span></li>
+     <li><var>hasARenderingOpportunity</var> is false</li>
     </ul>
 
-    <p>then for each <span>browsing context</span>, run the steps in the <span>start an idle period
-    algorithm</span>, passing the <code>Window</code> associated with that <span>browsing
-    context</span>. <ref spec="REQUESTIDLECALLBACK"></p>
-   </li>
-
-   <li>
-    <p>Report the duration of the <span>update the rendering</span> step by performing the
-    following steps:</p>
-
-    <ol>
-     <li><p>Let <var>rendering end time</var> be the <span>current high resolution
-     time</span>.</p></li>
-
-     <li><p>Let <var>top-level browsing contexts</var> be the set of all <span data-x="top-level
-     browsing context">top-level browsing contexts</span> of all <span>fully active</span>
-     <code>Document</code>s in <var>docs</var>.</p></li>
-
-     <li><p><span>Report long tasks</span>, passing in <var>now</var> (repurposed as meaning the
-     beginning of the <span>update the rendering</span> step), <var>rendering end time</var>, and
-     <var>top-level browsing contexts</var>.</p></li>
-    </ol>
+    <p>then for each <code>Window</code> object whose whose <span>relevant agent</span>'s
+    <span>event loop</span> is this event loop, run the <span>start an idle period
+    algorithm</span>, passing the <code>Window</code>. <ref spec="REQUESTIDLECALLBACK"></p>
    </li>
 
    <li>