[content shell] add a getPropertyDescriptor trap to the test runner

content/shell/webkit_test_runner.js

Index: content/shell/webkit_test_runner.js
diff --git a/content/shell/webkit_test_runner.js b/content/shell/webkit_test_runner.js
index 4b9f386cb394c98638ffa8c1ea8d2f9eafb582aa..8865ec96cd6383c8ef5e019f41928c1bbf638538 100644
--- a/content/shell/webkit_test_runner.js
+++ b/content/shell/webkit_test_runner.js
@@ -25,6 +25,10 @@ var textInputController = textInputController || {};
       get: function(receiver, property) {
         NotImplemented(name, property);
         return function() {}
+      },
+      getPropertyDescriptor: function(property) {
+        NotImplemented(name, property);
+        return undefined;
       }
     }
     return Proxy.create(handler);