Tie BarProp object lifetime to the Window object

Also describe what happens when the browsing context is discarded.

Tests: web-platform-tests/wpt#15815.

Fixes #2579.

source

@@ -78443,8 +78443,7 @@ interface <dfn data-export="" data-dfn-type="interface">Window</dfn> : <span>Eve
   [Replaceable] readonly attribute <span>BarProp</span> <span data-x="dom-window-personalbar">personalbar</span>;
   [Replaceable] readonly attribute <span>BarProp</span> <span data-x="dom-window-scrollbars">scrollbars</span>;
   [Replaceable] readonly attribute <span>BarProp</span> <span data-x="dom-window-statusbar">statusbar</span>;
-  [Replaceable] readonly attribute <span>BarProp</span> <span data-x="dom-window-toolbar">toolbar</span>;<!--
-  [Replaceable] readonly attribute <span>BarProp</span> <span data-x="dom-window-directories">directories</span>; // legacy (Gecko-only) -->
+  [Replaceable] readonly attribute <span>BarProp</span> <span data-x="dom-window-toolbar">toolbar</span>;
   attribute DOMString <span data-x="dom-window-status">status</span>;
   void <span data-x="dom-window-close">close</span>();
   readonly attribute boolean <span data-x="dom-window-closed">closed</span>;
@@ -79203,7 +79202,6 @@ interface <dfn>BarProp</dfn> {
 };</code></pre>
 
   <dl class="domintro">
-
    <dt><var>window</var> . <code subdfn data-x="dom-window-locationbar">locationbar</code> . <code subdfn data-x="dom-BarProp-visible">visible</code></dt>
    <dd>
     <p>Returns true if the location bar is visible; otherwise, returns false.</p>
@@ -79234,45 +79232,45 @@ interface <dfn>BarProp</dfn> {
    <dd>
     <p>Returns true if the toolbar is visible; otherwise, returns false.</p>
    </dd>
-
   </dl>
 
   <div w-nodev>
 
-  <p>The <dfn data-x="dom-BarProp-visible">visible</dfn> attribute, on getting, must return either
-  true or a value determined by the user agent to most accurately represent the visibility state of
-  the user interface element that the object represents, as described below.</p>
+  <p>The <dfn data-x="dom-BarProp-visible">visible</dfn> attribute's getter must run these
+  steps:</p>
 
-  <p>The following <code>BarProp</code> objects exist for each <code>Document</code> object in a
-  <span>browsing context</span>. Some of the user interface elements represented by these objects
-  might have no equivalent in some user agents; for those user agents, except when otherwise
-  specified, the object must act as if it was present and visible (i.e. its <code
-  data-x="dom-BarProp-visible">visible</code> attribute must return true).</p>
+  <ol>
+   <li><p>If this <code>BarProp</code> object's <span>relevant global object</span>'s <span
+   data-x="window bc">browsing context</span> is null, then return false.
 
-  <dl>
+   <li><p>If the user agent does not have a user interface element that the object represents, as
+   described below, then return true.</p></li>
 
-   <dt><dfn>The location bar <code>BarProp</code> object</dfn></dt>
+   <li><p>Return true or a value determined by the user agent to most accurately represent the
+   visibility state of the user interface element that the object represents, as described
+   below.</p></li>
+  </ol>
 
+  <p>The following <code>BarProp</code> objects must exist for each <code>Window</code> object:</p>
+
+  <dl>
+   <dt><dfn>The location bar <code>BarProp</code> object</dfn></dt>
    <dd>Represents the user interface element that contains a control that displays the
    <span>URL</span> of the <span>active document</span>, or some similar interface concept.</dd>
 
    <dt><dfn>The menu bar <code>BarProp</code> object</dfn></dt>
-
    <dd>Represents the user interface element that contains a list of commands in menu form, or some
    similar interface concept.</dd>
 
    <dt><dfn>The personal bar <code>BarProp</code> object</dfn></dt>
-
    <dd>Represents the user interface element that contains links to the user's favorite pages, or
    some similar interface concept.</dd>
 
    <dt><dfn>The scrollbar <code>BarProp</code> object</dfn></dt>
-
    <dd>Represents the user interface element that contains a scrolling mechanism, or some similar
    interface concept.</dd>
 
    <dt><dfn>The status bar <code>BarProp</code> object</dfn></dt>
-
    <dd>Represents a user interface element found immediately below or after the document, as
    appropriate for the user's media, which typically provides information about ongoing network
    activity or information about elements that the user's pointing device is current indicating. If
@@ -79281,14 +79279,12 @@ interface <dfn>BarProp</dfn> {
    data-x="dom-BarProp-visible">visible</code> attribute may return false).</dd>
 
    <dt><dfn>The toolbar <code>BarProp</code> object</dfn></dt>
-
    <dd>Represents the user interface element found immediately above or before the document, as
    appropriate for the user's media, which typically provides <span>session history</span> traversal
    controls (back and forward buttons, reload buttons, etc). If the user agent has no such user
    interface element, then the object may act as if the corresponding user interface element was
    absent (i.e. its <code data-x="dom-BarProp-visible">visible</code> attribute may return
    false).</dd>
-
   </dl>
 
   <p>The <dfn><code data-x="dom-window-locationbar">locationbar</code></dfn> attribute must return
@@ -79309,11 +79305,6 @@ interface <dfn>BarProp</dfn> {
   <p>The <dfn><code data-x="dom-window-toolbar">toolbar</code></dfn> attribute must return <span>the
   toolbar <code>BarProp</code> object</span>.</p>
 
-<!--
-  <p>For legacy reasons, the <dfn><code data-x="dom-window-directories">directories</code></dfn>
-  attribute must also return <span>the personal bar <code>BarProp</code> object</span>.</p>
--->
-
   <hr>
 
   <p>For historical reasons, the <dfn><code data-x="dom-window-status">status</code></dfn> attribute