Chrome OS menu which is the first tab is not directly accessible on the Chromium OS. Even it you enter its address, which is http://welcome-cros.appspot.com/menu, you won’t be able to access the Menu. However, there is a workaround –

• Right click on the Google Chrome Browser icon on your desktop.
• Select “Properties”
• Look for “Target”
• In the  ”Target” box, after chrome.exe” put a space, and add the following line of code
• -user-agent=”Mozilla/5.0 (X11; U; CrOS i686 9.10; en-US) AppleWebKit/532.5 (KHTML, like Gecko) Chrome/4.0.253.0 Safari/532.5″ -pinned-tab-count=1
• Now, Click “Apply” and then “OK”
• Now go to “Options” menu in Google Chrome settings.
• Under “Home Page”, select ” Open This Page”
• Enter http://welcome-cros.appspot.com/menu
• Hit “close”
• Restart your Chrome browser
• That’s it

Thanks Kamal for the tip!