Not receiving Channel Id from GCM of Chrome

Not receiving Channel Id from GCM of Chrome

I'm following this example:
https://github.com/GoogleChrome/chrome-app-samples/tree/master/push-guestbook/guestbook-app
Just that my manifest has no app but browser_action:
{
"name": "Demo",
"version": "1.0",
"manifest_version": 2,
"description": "This is a demo",
"browser_action":{
"default_popup":"popup.html"
},
"background_page": "background.html",
"minimum_chrome_version": "23",
"background":{
"scripts":["Guestbook.js","background.js"]
},
"key": "xyz",
"content_scripts": [{
"matches": ["http://*/*"],
"js": ["jquery.js","content.js"]
}],
"permissions": [ "<all_urls>",
"http://*/*", "https://*/*",
"storage",
"tabs",
"http://localhost:3000/*",
"https://accounts.google.com/o/oauth2/token",
"https://www.googleapis.com/chromewebstore/v1.1/notifications",
"pushMessaging",
"notifications",
"contextMenus" ],
"web_accessible_resources":[
"content.js"
]
}
Everything else is the same for me, and I just don't get any channel Id
from the GCM servers. Where am I going wrong?