bindings: Supports [LenientThis] extended attributes.

LayoutTests/webexposed/resources/global-interface-listing.js

 if (self.importScripts) {
     importScripts('../../resources/js-test.js');
 
     if (!self.postMessage) {
         // Shared worker.  Make postMessage send to the newest client, which in
         // our tests is the only client.
 
         // Store messages for sending until we have somewhere to send them.
         self.postMessage = function(message) {
             if (typeof self.pendingMessages === "undefined")
@@ skipping 23 matching lines @@
 // FIXME: List interfaces with NoInterfaceObject specified in their IDL file.
 debug('[INTERFACES]')
 var interfaceNames = Object.getOwnPropertyNames(this).filter(isConstructor);
 interfaceNames.sort();
 interfaceNames.forEach(function(interfaceName) {
     debug('interface ' + interfaceName);
     var propertyStrings = [];
     var prototype = this[interfaceName].prototype;
     Object.getOwnPropertyNames(prototype).forEach(function(propertyName) {
         var descriptor = Object.getOwnPropertyDescriptor(prototype, propertyName);
-        if (typeof descriptor.value !== 'undefined') {
+        if ('value' in descriptor) {
             var type = typeof descriptor.value === 'function' ? 'method' : 'attribute';
             propertyStrings.push('    ' + type + ' ' + propertyName);
         } else {
             if (descriptor.get)
                 propertyStrings.push('    getter ' + propertyName);
             if (descriptor.set)
                 propertyStrings.push('    setter ' + propertyName);
         }
     });
     propertyStrings.sort().forEach(debug);
 });
 
 if (isWorker())
     finishJSTest();