bindings: Supports serializer for PerformanceTiming.

LayoutTests/fast/dom/Window/window-properties-performance.html

 <p>This test dumps all of the properties that are reachable from the window.performance object, along with their types.</p>
 <hr>
 <pre id="pre"></pre>
 
 <script>
 if (window.testRunner)
     testRunner.dumpAsText();
     
 var logBuffer = [];
 function log(s)
@@ skipping 73 matching lines @@
     array.sort();
     for (var i = 0; i < array.length; i++) {
         var property = array[i];
         logValue(objectName + "." + property);
     }
 }
 
 logValue('window.performance');
 window.performance.timing = 'timing is not replaceable';
 logValue('window.performance.timing');
+// PerformanceTiming supports a serializer.
+var jsonizedTiming = JSON.parse(JSON.stringify(window.performance.timing));
+logValue('jsonizedTiming');
 window.performance.navigation = 'navigation is not replaceable';
 logValue('window.performance.navigation');
 window.performance = 'performance is replaceable';
 logValue('window.performance');
 flushLog();
 </script>