Use ExecuteJavascriptInWebFrameNotifyResult to return results even in error condition

chrome/test/data/webui/sample_downloads.js

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Sample tests that exercise the test JS library and show how this framework
 // could be used to test the downloads page.
 function testAssertFalse() {
   assertFalse(false);
 }
 
+function FAILS_testAssertFalse() {
+  assertFalse(true);
+  assertFalse(false);
+}
+
 function testInitialFocus() {
   assertTrue(document.activeElement.id == 'term', '');
 }
 
 function testConsoleError() {
   console.error('checking console.error call causes failure.');
 }