EditorUtility.SetDirty  

static function SetDirty (target : Object) : void

Description

Marks target object as dirty.

Unity internally uses the dirty flag to find out when assets have changed and need to be saved to disk.

E.g. if you modify a prefab's MonoBehaviour or ScriptableObject variables, you must tell Unity that the value has changed. Unity builtin components internally call SetDirty whenever a property changes. MonoBehaviour or ScriptableObject don't do this automatically so if you want your value to be saved you need to call SetDirty.