Below is the Google OAuth Scope list. Scope is required when you are making OAuth Request.
OAuth Request of Google Cloud Messging
OAuth request for Google Cloud Messaging: https://accounts.google.com/o/oauth2/auth?response_type=code&client_id=150002918248.apps.googleusercontent.com&redirect_uri=http://hayageek.com/examples/google-chrome-gcm/oauth.php&scope=https://www.googleapis.com/auth/gcm_for_chrome&access_type=offline
OAuth request for Youtube:https://accounts.google.com/o/oauth2/auth?response_type=code&client_id=150002918248.apps.googleusercontent.com&redirect_uri=http://hayageek.com/examples/google-chrome-gcm/oauth.php&scope=https://gdata.youtube.com&access_type=offline