You could use the little known UI Automation API, like this:

static void CloseAllChromeBrowsers()
{
    foreach (Process process in Process.GetProcessesByName("chrome"))
    {
        if (process.MainWindowHandle == IntPtr.Zero) // some have no UI
            continue;

        AutomationElement element = AutomationElement.FromHandle(process.MainWindowHandle);
        if (element != null)
        {
            ((WindowPattern)element.GetCurrentPattern(WindowPattern.Pattern)).Close();
        }
    }
}