oauth2 not happening

gistfile1.js

//in popup.js
var google = new OAuth2('google', {
    client_id: '17755888930840',
    client_secret: 'b4a5741bd3d6de6ac591c7b0e279c9f',
    api_scope: 'https://www.googleapis.com/auth/tasks'
});


function authorize() {
    google.authorize(checkAuthorized);
}

function checkAuthorized() {
    console.log('checkAuthorized');
    if (google.hasAccessToken()) {
        // do nothing all is ok                                                                                                         
    } else {
        authorize();
    }

}

// in manifest.json


    "content_scripts": [
        {
            "matches": ["http://*/*"],
            "js" : ["js/oncopy.js"]
        },
        {
            "matches": ["http://www.google.com/robots.txt*"],
            "js": ["oauth2/oauth2_inject.js"],
            "run_at": "document_start"
        }
    ],