Introducing self.origin, a reliable way to get the origin of a global

Fixes https://www.w3.org/Bugs/Public/show_bug.cgi?id=28801.

source

@@ -87405,6 +87405,8 @@ interface <dfn>DocumentAndElementEventHandlers</dfn> {
 
 [NoInterfaceObject, Exposed=(Window,Worker)]
 interface <dfn>WindowOrWorkerGlobalScope</dfn> {
+  [Replaceable] readonly attribute USVString <span data-x="dom-origin">origin</span>;
+
   // base64 utility methods
   DOMString <span data-x="dom-btoa">btoa</span>(DOMString data);
   DOMString <span data-x="dom-atob">atob</span>(DOMString data);
@@ -87428,6 +87430,18 @@ interface <dfn>WindowOrWorkerGlobalScope</dfn> {
           http://software.hixie.ch/utilities/js/live-dom-viewer/saved/1229
   -->
 
+  <dl class="domintro">
+
+   <dt><var>origin</var> = self . <code subdfn data-x="dom-origin">origin</code></dt>
+
+   <dd><p>Returns the global object's <span>origin</span>, serialised as string.</p></dd>
+
+  </dl>
+
+  <p>The <dfn data-x="dom-origin"><code>origin</code></dfn> attribute's getter must return this
+  object's <span>relevant setting object</span>'s <span>origin</span>, <span data-x="Unicode
+  serialisation of an origin">serialised</span>.</p>
+
 
   <h3 id="atob">Base64 utility methods</h3>