Issue #524 'creator context security' (#772)

* Issue #524 'creator context security'
* Port whatwg/html@a5853c3

Note, workers change in #1561 out of scope in HTML 5.2 - needs to
go into workers spec.

sections/browsers.include

@@ -59,11 +59,30 @@
   <a>creator browsing context</a>. Otherwise, the <a>browsing context</a> has no
   <a>creator browsing context</a>.
 
-  If a <a>browsing context</a> <var>A</var> has a <a>creator browsing context</a>, then the
-  <dfn>creator origin</dfn>, <dfn>creator URL</dfn>, and <dfn>creator base URL</dfn> are the
-  [=concept/origin=], [=document url|URL=], and <a lt='document base URL'>base URL</a>, respectively, of
-  the {{Document}} that was the <a>active document</a> of that <a>creator browsing context</a> at
-  the time <var>A</var> was created.
+  <p>If a [=browsing context=] <var>context</var> has a [=creator browsing context=]
+  <var>creator</var>, it also has the following properties. In what follows, let
+  <var>creator document</var> be <var>creator</var>'s [=active document=] at the time
+  <var>context</var> is created:</p>
+
+  <dl>
+   <dt><dfn>creator origin</dfn></dt>
+   <dd>|creator document|'s [=concept/origin=]</dd>
+
+   <dt><dfn>creator URL</dfn></dt>
+   <dd>|creator document|'s [=document url|URL=]</dd>
+
+   <dt><dfn>creator base URL</dfn></dt>
+   <dd>|creator document|'s [=base URL=]</dd>
+
+   <dt><dfn>creator referrer policy</dfn></dt>
+   <dd>|creator document|'s [=referrer policy=]</dd>
+
+   <dt><dfn>creator context security</dfn></dt>
+   <dd>The result of executing <span>Is environment settings object a secure context?</span> on
+   |creator document|'s [=relevant settings object=]</dd>
+  </dl>
+
+  <div w-nodev>
 
   To <dfn lt="creating a new browsing context|create a new browsing context">create a new browsing context</dfn>: