Improve fidelity of XHR progress events.

LayoutTests/fast/xmlhttprequest/xmlhttprequest-get.xhtml

 <?xml version="1.0"?>
 <!-- 
    - The contents of this file are subject to the Mozilla Public
    - License Version 1.1 (the "License"); you may not use this file
    - except in compliance with the License. You may obtain a copy of
    - the License at http://www.mozilla.org/MPL/
    - 
    - Software distributed under the License is distributed on an "AS
    - IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
    - implied. See the License for the specific language governing
@@ skipping 26 matching lines @@
 }
 </style>
 <script type="text/javascript">
 var p = new XMLHttpRequest();
 
 if (window.testRunner) {
   testRunner.dumpAsText();
   testRunner.waitUntilDone();
 }
 
+// Some properties do not have stable/guaranteed values;
+// emit default values for these.
+var propertiesWithDefaultValues = {loaded: 0, total: 0, position: 0, totalSize: 0};
+
 function myfunc(e)
 {
   document.getElementById("id1").firstChild.nodeValue = p.responseText;
   if (p.responseXML) {
     var s = new XMLSerializer();
     var d = p.responseXML;
     var str = s.serializeToString(d);
     document.getElementById("id2").firstChild.nodeValue = str;
   }
   document.getElementById("id3").firstChild.nodeValue = p.getAllResponseHeaders();
   document.getElementById("id4").firstChild.nodeValue = p.status;
   document.getElementById("id5").firstChild.nodeValue = p.statusText;
   document.getElementById("id6").firstChild.nodeValue = p.readyState;
   var propNames = new Array;
   for (prop in e) {
     if (prop != "timeStamp") {
         propNames.push(prop);
     }
   }
   propNames.sort();
   var eventProperties = "";
   for (i in propNames) {
         var prop = propNames[i];
-        eventProperties += prop + " : '" + e[prop] + "'\n";
+        var value = (prop in propertiesWithDefaultValues) ? propertiesWithDefaultValues[prop] : e[prop];
+        eventProperties += prop + " : '" + value + "'\n";
   }
-  
-  document.getElementById("id7").firstChild.nodeValue = 
+
+  document.getElementById("id7").firstChild.nodeValue =
     "Event object: " + e + "\n" +
     "Event properties:\n" + eventProperties;
 
   if (window.testRunner)
     testRunner.notifyDone();
 }
 
 p.onload = myfunc;
 p.open("GET", "resources/xmlhttprequest-get-data.xml");
 
@@ skipping 23 matching lines @@
 </div>
 <div class="box"><span class="boxheader">readyState</span>
 <pre id="id6">@@No result@@</pre>
 </div>
 <div class="box"><span class="boxheader">Event information</span>
 <pre id="id7">@@No result@@</pre>
 </div>
 
 </body>
 </html>