bindings: Fixes layouttests when moving attributes to prototype chains.

LayoutTests/webexposed/resources/element-instance-property-listing.js

 (function() {
 
 if (!window.internals) {
     testFailed('Test must be run with --expose-internals-for-testing flag.');
     return;
 }
 
 // FIXME(https://crbug.com/43394):
 // These properties should live in the element prototypes instead of on the individual instances.
 function listElementProperties(type) {
     debug('[' + type.toUpperCase() + ' NAMESPACE ELEMENT PROPERTIES]');
     var namespace = internals[type + 'Namespace']();
     debug('namespace ' + namespace);
     var tags = internals[type + 'Tags']();
     var tagProperties = {};
-    var isCommonProperty = null; // Will be a map containing the intersection of properties across all elements as keys.
+    var commonProperties = null; // Will be a map containing the intersection of properties across all elements as keys.
     tags.forEach(function(tag) {
         var element = document.createElement(tag, namespace);
         // We don't read out the property descriptors here to avoid the test timing out.
-        var properties = Object.getOwnPropertyNames(element).sort();
+        var properties = [];
+        for (var property in element) {
+            properties.push(property);
+        }
+        properties.sort();
         tagProperties[tag] = properties;
-        if (isCommonProperty === null) {
-            isCommonProperty = {};
+        if (commonProperties === null) {
+            commonProperties = {};
             properties.forEach(function(property) {
-                isCommonProperty[property] = true;
+                commonProperties[property] = true;
             });
         } else {
             var hasProperty = {};
             properties.forEach(function(property) {
                 hasProperty[property] = true;
             });
-            Object.getOwnPropertyNames(isCommonProperty).forEach(function(property) {
+            Object.getOwnPropertyNames(commonProperties).forEach(function(property) {
                 if (!hasProperty[property])
-                    delete isCommonProperty[property];
+                    delete commonProperties[property];
             });
         }
     });
     debug(escapeHTML('<common>'));
-    Object.getOwnPropertyNames(isCommonProperty).sort().forEach(function(property) {
+    Object.getOwnPropertyNames(commonProperties).sort().forEach(function(property) {
         debug('    property ' + property);
     });
     tags.forEach(function(tag) {
         debug(type + ' element ' + tag);
         tagProperties[tag].forEach(function(property) {
-            if (!isCommonProperty[property])
+            if (!(property in commonProperties))
                 debug('    property ' + property);
         });
     });
 }
 
 listElementProperties('html');
 listElementProperties('svg');
 
 })();