Set Icons for MonoBehaviours in DLLs

using UnityEngine;
using UnityEditor;

public class ChangeIcon : MonoBehaviour
{
    [MenuItem("Coding Jar/Test Icon")]
    static void TestIcon()
    {
        var assetPath = AssetDatabase.GetAssetPath( Selection.activeObject );
        Texture2D icon = AssetDatabase.LoadAssetAtPath( "Assets/Icon.png", typeof(Texture2D) ) as Texture2D;

#if USE_SETICONFOROBJECT_NONPERSISTENT
        // This will set the icon for every MonoBehaviour in the DLL, you can do this at start-up...
        var setIconForObject = Types.GetType( "UnityEditor.EditorGUIUtility", "UnityEditor" ).GetMethod( "SetIconForObject", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Static );
        foreach (var partObj in AssetDatabase.LoadAllAssetRepresentationsAtPath(assetPath) )
        {
            setIconForObject.Invoke( null, new object[] { partObj, icon } );
        }
#endif

        AssetImporter importer = AssetImporter.GetAtPath(assetPath);
        SerializedObject serObj = new SerializedObject( importer );
        var iconMapProperty = serObj.FindProperty( "m_IconMap" );
        if ( iconMapProperty.arraySize < 1 )
        {
            iconMapProperty.InsertArrayElementAtIndex(0);
        }

        var iconElementProperty = iconMapProperty.GetArrayElementAtIndex(0);
        var firstProperty = iconElementProperty.FindPropertyRelative( "first" );
        //firstProperty.stringValue = "THis should be the class name";

        var secondProperty = iconElementProperty.FindPropertyRelative( "second" );
        secondProperty.objectReferenceValue = icon;

        serObj.ApplyModifiedProperties();
        AssetDatabase.WriteImportSettingsIfDirty( assetPath );
    }
}