STEPS TO TEST:
TEST PASS: After the close button is clicked, you should see a dialog that reads:
Are you sure you want to navigate away from this page? onBeforeUnloadHandler return string is displayed here. Press OK to continue or Cancel to stay on the current page.
You should see the same dialog if you click the "Close" button in the main window.
TEST FAIL: No dialog (as described above) after clicking the "Close" button in the newly opened window, or in the main window.
Click the Open Window button. Once the new window is opened, close the new window by clicking the Close Window button (not the browser's close window icon).