Bug 1168823 - Repair XML syntax highlighting. r=jst

dom/base/test/file_bug590812-ref.xhtml

@@ -1,3 +1,3 @@
-<out><div id="top" xmlns="http://www.w3.org/1999/xhtml"><link href="chrome://global/content/xml/XMLPrettyPrint.css" type="text/css" rel="stylesheet"/><div id="header"><p>
+<out><div id="top" class="highlight" xmlns="http://www.w3.org/1999/xhtml"><link href="chrome://global/content/xml/XMLPrettyPrint.css" type="text/css" rel="stylesheet"/><div id="header"><p>
         This XML file does not appear to have any style information associated with it. The document tree is shown below.
       </p></div><div>&lt;<span class="start-tag">out</span>&gt;<span class="text">Here be sea hags</span>&lt;/<span class="end-tag">out</span>&gt;</div></div></out>

dom/xml/resources/XMLPrettyPrint.xml

@@ -8,7 +8,7 @@
 
   <binding id="prettyprint" bindToUntrustedContent="true">
 
-    <content><html:div id='top'/>
+    <content><html:div id='top' class="highlight"/>
       <html:span style="display: none;"><children/></html:span>
     </content>