RoleDefinitions.BreakInheritance 2013 CSOM API

I need to break permission level inheritance. The following works fine with the server API: SPWeb.RoleDefinitions.BreakInheritance(true, true)

Now I need to do the same with Sharepoint 2013 CSOM API. The method BreakInheritance seems not to be available for RoleDefinitions.