Don't throw when popover/dialog is in requested state

This patch makes the following changes:
- Don't throw exceptions when showPopover or hidePopover is called and
  the popover is already in the requested state.
- Don't throw exceptions when dialog.showModal, dialog.show, or
  dialog.close is called and the dialog is already in the
  requested state.
- Throw exceptions when trying to switch between modal and non-modal
  dialog modes via dialog.showModal or dialog.show.

Fixes whatwg#9045

source

@@ -60034,8 +60034,11 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
   method steps are:</p>
 
   <ol>
+   <li><p>If <span>this</span> has an <code data-x="attr-dialog-open">open</code> attribute and the
+   <span>is modal</span> flag of <span>this</span> is true, then return.</p></li>
+
    <li><p>If <span>this</span> has an <code data-x="attr-dialog-open">open</code> attribute, then
-   return.</p></li>
+   throw an <span>"<code>InvalidStateError</code>"</span> <code>DOMException</code>.</p></li>
 
    <li><p>If <span>this</span> is in the <span data-x="popover-showing-state">popover showing
    state</span>, then throw an <span>"<code>InvalidStateError</code>"</span>
@@ -60054,6 +60057,9 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
   data-x="dom-dialog-showModal">showModal()</code></dfn> method steps are:</p>
 
   <ol>
+   <li><p>If <span>this</span> has an <code data-x="attr-dialog-open">open</code> attribute and the
+   <span>is modal</span> flag of <span>this</span> is true, then return.</p></li>
+
    <li><p>If <span>this</span> has an <code data-x="attr-dialog-open">open</code> attribute, then
    throw an <span>"<code>InvalidStateError</code>"</span> <code>DOMException</code>.</p></li>
 
@@ -82130,8 +82136,8 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
       <p class="note"><span>Check popover validity</span> is called again because running <span
       data-x="hide-all-popovers-until">hide all popovers until</span> above could have fired the
       <code data-x="event-beforetoggle">beforetoggle</code> event, and an event handler could have
-      disconnected this element or called <code data-x="dom-showPopover">showPopover()</code> on
-      this element.</p>
+      disconnected this element or changes its <code data-x="attr-popover">popover</code>
+      attribute.</p>
      </li>
     </ol>
    </li>
@@ -82554,18 +82560,27 @@ dictionary <dfn dictionary>DragEventInit</dfn> : <span>MouseEventInit</span> {
     </ol>
    </li>
 
+   <li><p>If <var>element</var> is not <span>connected</span>, then throw a
+   <span>"<code>InvalidStateError</code>"</span> <code>DOMException</code>.</p></li>
+
    <li>
     <p>If one of the following conditions is true</p>
 
     <ul>
-     <li><p><var>element</var> is not <span>connected</span></p></li>
-
      <li><p><var>expectedToBeShowing</var> is true and <var>element</var>'s <span>popover visibility
      state</span> is not <span data-x="popover-showing-state">showing</span></p></li>
 
      <li><p><var>expectedToBeShowing</var> is false and <var>element</var>'s <span>popover
      visibility state</span> is not <span data-x="popover-hidden-state">hidden</span></p></li>
+    </ul>
+
+    <p>then return false.</p>
+   </li>
 
+   <li>
+    <p>If one of the following conditions is true</p>
+
+    <ul>
      <li><p><var>element</var> is a <code>dialog</code> element and has an <code
      data-x="attr-details-open">open</code> attribute</p></li>