Quite safe*, discounting any cold boot attack or any vulnerability that allows bypass of the OS's lock screen.
Chrome encrypts its cookies, using a password based encryption scheme. In Windows, this is based upon the Data Protection API. This means that anyone who gains access to the laptop by either changing the Windows password using a tool such as chntpw, or if they try to access the hard drive from another operating system to get access to the cookie DB, they will not be able to easily extract your session cookies with Google. So while there are various methods of bypassing the Windows login screen, without the password being available in memory to decrypt Chrome's cookies, this does not really aid an attacker.
There are also implementations for Linux and OS X. See also: Key for chromium's encrypted cookies store in Linux is "peanuts" [no longer].
Of course, at the end of the day this will employ Password Based Encryption of the cookie data. So make sure that your logon account is protected by a strong password with enough entropy to give you enough time to logout other sessions using another device before your OS password can be cracked. If your password has 64 bits of entropy or more, you will only have the insurance claim for the laptop to worry about.
* as said in my answer - only as safe as your password is secure.