Add notRestoredReasons to PerformanceNavigationTiming attribute

index.html

@@ -372,6 +372,7 @@ <h3>
             readonly        attribute NavigationTimingType type;
             readonly        attribute unsigned short       redirectCount;
             readonly        attribute DOMHighResTimeStamp  criticalCHRestart;
+            readonly        attribute NotRestoredReasons?  notRestoredReasons;
             [Default] object toJSON();
         };
         </pre>
@@ -393,6 +394,9 @@ <h3>
         <p>A <a>PerformanceNavigationTiming</a> has an associated
           {{DOMHighResTimeStamp}} <a data-dfn-for="PerformanceNavigationTiming"><dfn>`Critical-CH` restart time</dfn></a>.
 
+        <p>A <a>PerformanceNavigationTiming</a> has an associated
+        {{NotRestoredReasons}} <a data-dfn-for="PerformanceNavigationTiming"><dfn>not restored reasons</dfn></a>.
+
         <p>A {{PerformanceNavigationTiming}} has an associated null or [=service worker timing info=] 
         <dfn data-dfn-for="PerformanceNavigationTiming">service worker timing</dfn>.
         </p>
@@ -502,6 +506,9 @@ <h3>
             the moment the redirection part of the navigation was restarted.
           </p>
         </div>
+        <p data-dfn-for='PerformanceNavigationTiming'>
+         The <dfn>notRestoredReasons</dfn> getter steps are to return |this|'s
+        <span>not restored reasons</span>.</p>
         <p>
           The <dfn>toJSON()</dfn> method runs the [=default toJSON steps=] for [=this=].
         </p>
@@ -615,6 +622,10 @@ <h2>Creating a navigation timing entry</h2>
         <li>Set |document|'s <span>navigation timing entry</span> to |navigationTimingEntry|.
         <li>Set |navigationTimingEntry|'s <a data-for="PerformanceNavigationTiming">`Critical-CH` restart time</a>
         to |criticalCHRestart|.
+        <li>If document is the outermost main frame's document, set |navigationTimingEntry|'s
+        <a data-for="PerformanceNavigationTiming">not restored reasons</a> to the result of
+        creating a NotRestoredReasons object given |document|'s node navigable's active session
+        history entry's document state's not restored reasons and realm.</li>
         <li>add |navigationTimingEntry| to |global|'s
         <a data-cite='performance-timeline-2#dfn-performance-entry-buffer'>performance entry buffer</a>.
       </ol>