Centralize checks for <a>, <area>, <form>, and <link>

Require that they are all connected to a document that is fully
active. There is enough difference between implementations that this
appears to be web compatible.

Tests:

* web-platform-tests/wpt#5758
* web-platform-tests/wpt#5759
* web-platform-tests/wpt#5761

Fixes #2615.

source

@@ -13400,19 +13400,10 @@ interface <dfn>HTMLLinkElement</dfn> : <span>HTMLElement</span> {
   <p>User agents could also include other information, such as the type of the resource (as given by
   the <code data-x="attr-link-type">type</code> attribute).</p>
 
+  <!-- c.f. <a> and <area>'s similar sections -->
   <p>The <span>activation behavior</span> of <code>link</code> elements that create <span
-  data-x="hyperlink">hyperlinks</span> is to run the following steps:</p>
-
-  <ol><!-- c.f. <a> and <area>'s similar sections -->
-
-   <li><p>If the <code>link</code> element's <span>node document</span> is not <span>fully
-   active</span>, then abort these steps.</p></li>
-
-   <li><p><span data-x="following hyperlinks">Follow the hyperlink</span> created by the
-   <code>link</code> element.</p></li>
-
-  </ol>
-
+  data-x="hyperlink">hyperlinks</span> is to <span data-x="following hyperlinks">follow the
+  hyperlink</span> created by the <code>link</code> element.</p>
 
 
 
@@ -19182,12 +19173,7 @@ interface <dfn>HTMLAnchorElement</dfn> : <span>HTMLElement</span> {
   <p>The <span>activation behavior</span> of <code>a</code> elements that create <span
   data-x="hyperlink">hyperlinks</span> is to run the following steps:</p>
 
-  <ol><!-- c.f. <area>'s similar section, also <link>'s -->
-
-   <li><p>If the <code>a</code> element's <span>node document</span> is not <span>fully active</span>, then abort these steps.</p></li>
-   <!-- https://software.hixie.ch/utilities/js/live-dom-viewer/?saved=2033 -->
-   <!-- https://www.hixie.ch/tests/adhoc/html/navigation/iframe/002.html -->
-
+  <ol><!-- c.f. <link> and <area>'s similar section -->
    <li>
 
     <p>If the user has not indicated a specific <span>browsing context</span> for following the
@@ -22768,11 +22754,19 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
 
   <h4>Following hyperlinks</h4>
 
+  <p>An element <var>element</var> <dfn>cannot navigate</dfn> if <var>element</var>'s <span>node
+  document</span> is not <span>fully active</span> or <var>element</var> is not
+  <span>connected</span>.
+
+  <p class="note">This is also used by <span data-x="concept-form-submit">form submission</span> for
+  the <code>form</code> element.</p>
+
   <p>When a user <dfn data-x="following hyperlinks">follows a hyperlink</dfn> created by an element
   <var>subject</var>, optionally with a <var>hyperlink suffix</var>, the user agent must run the
   following steps:</p>
 
   <ol>
+   <li><p>If <var>subject</var> <span>cannot navigate</span>, then return.</p></li>
 
    <li><p>Let <var>replace</var> be false.</p></li>
 
@@ -22880,6 +22874,7 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
   run the following steps:</p>
 
   <ol>
+   <li><p>If <var>subject</var> <span>cannot navigate</span>, then return.</p></li>
 
    <li><p><span data-x="parse a url">Parse</span> the <span>URL</span> given by
    <var>subject</var>'s <code data-x="attr-hyperlink-href">href</code> attribute, relative to
@@ -38254,11 +38249,7 @@ interface <dfn>HTMLAreaElement</dfn> : <span>HTMLElement</span> {
   <p>The <span>activation behavior</span> of <code>area</code> elements is to run the following
   steps:</p>
 
-  <ol><!-- c.f. <a>'s similar section -->
-
-   <li><p>If the <code>area</code> element's <span>node document</span> is not <span>fully active</span>,
-   then abort these steps.</p></li>
-
+  <ol><!-- c.f. <link> and <a>'s similar section -->
    <li>
 
     <p>If the user has not indicated a specific <span>browsing context</span> for following the
@@ -55289,14 +55280,12 @@ fur
   following steps:</p>
 
   <ol>
+   <li><p>If <var>form</var> <span>cannot navigate</span>, then return.</p></li>
 
-   <li><p>Let <var>form document</var> be the <var>form</var>'s
-   <span>node document</span>.</p></li>
+   <li><p>Let <var>form document</var> be <var>form</var>'s <span>node document</span>.</p></li>
 
-   <li id="sandboxSubmitBlocked"><p>If <var>form document</var> is not <span>connected</span>, has
-   no associated <span data-x="concept-document-bc">browsing context</span>, or its <span>active
-   sandboxing flag set</span> has its <span>sandboxed forms browsing context flag</span> set, then
-   abort these steps without doing anything.</p></li>
+   <li id="sandboxSubmitBlocked"><p>If <var>form document</var>'s <span>active sandboxing flag
+   set</span> has its <span>sandboxed forms browsing context flag</span> set, then return.</p></li>
 
    <li><p>Let <var>form browsing context</var> be the <span data-x="concept-document-bc">browsing
    context</span> of <var>form document</var>.</p></li>