chrome.windows.create

I try to create a popup window from an addon, but the Google documentation seems insufficient.

Code:

var opciones ={
    'url': url, 
    'width':400, 
    'height':300,
    'type': 'popup'
};

chrome.windows.create(opciones, function(window) {
    console.log("ventana creada");
});

When I execute it, it says:

 Uncaught TypeError: Cannot read property 'create' of undefined

I really do not know where the fault could be.