Fix #47: not all settings objects have a responsible document anymore

The reason we can remove this check is because workers already only run
when the document that created them is fully active. (It’s just that
such a document is no longer the responsible document.)

(Service workers are not a concern since XMLHttpRequest is not exposed
there.)

Overview.html

@@ -527,14 +527,13 @@ <h4 id="the-open()-method"><span class="secno">4.5.1 </span>The <code title="">o
 
 <p>The
 <dfn id="dom-xmlhttprequest-open" title="dom-XMLHttpRequest-open"><code>open(<var title="">method</var>, <var title="">url</var>, <var title="">async</var>, <var title="">username</var>, <var title="">password</var>)</code></dfn>
-method must run these steps:
+method, when invoked, must run these steps:
 
 <ol>
- <li><p>If <a href="#concept-xmlhttprequest-settings-object" title="concept-XMLHttpRequest-settings-object">settings object</a>'s
- <a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#responsible-document">responsible document</a> is not
+ <li><p>If <a href="#concept-xmlhttprequest-settings-object" title="concept-XMLHttpRequest-settings-object">settings object</a> has a
+ <a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/webappapis.html#responsible-document">responsible document</a> and it is <em>not</em>
  <a class="external" data-anolis-spec="html" href="https://html.spec.whatwg.org/multipage/browsers.html#fully-active">fully active</a>,
- <a class="external" data-anolis-spec="webidl" href="https://heycam.github.io/webidl/#dfn-throw" title="throw">throw</a> an
- <code>InvalidStateError</code> exception.
+ <a class="external" data-anolis-spec="webidl" href="https://heycam.github.io/webidl/#dfn-throw" title="throw">throw</a> an <code>InvalidStateError</code> exception.
 
  <li><p>Set <var title="">base</var> to
  <a href="#concept-xmlhttprequest-settings-object" title="concept-XMLHttpRequest-settings-object">settings object</a>'s

Overview.src.html

@@ -479,14 +479,13 @@ <h4>The <code title>open()</code> method</h4>
 
 <p>The
 <dfn id="dom-xmlhttprequest-open" title="dom-XMLHttpRequest-open"><code>open(<var title>method</var>, <var title>url</var>, <var title>async</var>, <var title>username</var>, <var title>password</var>)</code></dfn>
-method must run these steps:
+method, when invoked, must run these steps:
 
 <ol>
- <li><p>If <span title=concept-XMLHttpRequest-settings-object>settings object</span>'s
- <span data-anolis-spec=html>responsible document</span> is not
+ <li><p>If <span title=concept-XMLHttpRequest-settings-object>settings object</span> has a
+ <span data-anolis-spec=html>responsible document</span> and it is <em>not</em>
  <span data-anolis-spec=html>fully active</span>,
- <span data-anolis-spec=webidl title=throw>throw</span> an
- <code>InvalidStateError</code> exception.
+ <span data-anolis-spec=webidl title=throw>throw</span> an <code>InvalidStateError</code> exception.
 
  <li><p>Set <var title>base</var> to
  <span title=concept-XMLHttpRequest-settings-object>settings object</span>'s