Integrate with requestIdleCallback

This adds a hook to the event loop's processing model to define when the
start of an idle period should begin. This deals with the issue in
w3c/requestidlecallback#70 and calls directly into the "start an idle
period" algorithm, instead of that algorithm having to having to spin
the event loop.

Follows w3c/requestidlecallback#75. Closes #3570 by superceding it; this
simpler version avoids needing to track notifying above rejected
promises or cleaning up IDB transactions.

Author: rmcilroy

source

@@ -4198,6 +4198,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
 
     <ul class="brief">
      <li><dfn data-x-href="https://w3c.github.io/requestidlecallback/#the-requestidlecallback-method"><code>requestIdleCallback()</code></dfn></li>
+     <li><dfn data-x-href="https://w3c.github.io/requestidlecallback/#start-an-idle-period-algorithm">start an idle period algorithm</dfn></li>
     </ul>
    </dd>
 
@@ -89336,6 +89337,15 @@ dictionary <dfn>PromiseRejectionEventInit</dfn> : <span>EventInit</span> {
     </ol>
    </li>
 
+   <li><p>If this is a <span>browsing context</span> <span>event loop</span> (as opposed to a <a
+   href="#workers">worker</a> <span>event loop</span>), and there are no <span
+   data-x="concept-task">tasks</span> in the <span>event loop</span>'s <span data-x="task
+   queue">task queues</span>, and the <span>event loop</span>'s <span>microtask queue</span> is
+   empty, and none of the <span data-x="browsing context">browsing contexts</span> have a
+   <span>rendering opportunity</span>, 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>
@@ -121256,7 +121266,7 @@ INSERT INTERFACES HERE
    <dd><cite><a href="https://w3c.github.io/webappsec-referrer-policy/">Referrer Policy</a></cite>, J. Eisinger, E. Stark. W3C.</dd>
 
    <dt id="refsREQUESTIDLECALLBACK">[REQUESTIDLECALLBACK]</dt>
-   <dd>(Non-normative) <cite><a href="https://w3c.github.io/requestidlecallback/">Cooperative Scheduling of Background Tasks</a></cite>, R. McIlry, I. Grigorik. W3C.</dd>
+   <dd><cite><a href="https://w3c.github.io/requestidlecallback/">Cooperative Scheduling of Background Tasks</a></cite>, R. McIlroy, I. Grigorik. W3C.</dd>
 
    <dt id="refsRESOURCEHINTS">[RESOURCEHINTS]</dt>
    <dd><cite><a href="https://w3c.github.io/resource-hints/">Resource Hints</a></cite>, I. Grigorik. W3C.</dd>