Unity's coroutines extensions

CoroutineExtensions.cs

using System;
using System.Collections;
using UnityEngine;

public static class CoroutineExtensions
{
    public static Coroutine Then( this Coroutine self, Action action )
    {
        return DefaultCoroutineHost.Instance.StartCoroutine( ChainWithAction( self, action ) );
    }

    public static Coroutine Then( this Coroutine self, IEnumerator coroutine )
    {
        return DefaultCoroutineHost.Instance.StartCoroutine( ChainWithCoroutine( self, coroutine ) );
    }

    private static IEnumerator ChainWithCoroutine( Coroutine first, IEnumerator second )
    {
        yield return first;
        yield return DefaultCoroutineHost.Instance.StartCoroutine( second );
    }

    private static IEnumerator ChainWithAction( Coroutine coroutine, Action action )
    {
        yield return coroutine;
        action();
    }
}

DefaultCoroutineHost.cs

using Gamelogic.Extensions;
using UnityEngine;

public class DefaultCoroutineHost : GLMonoBehaviour
{
    private static DefaultCoroutineHost _instance;

    public static DefaultCoroutineHost Instance
    {
        get
        {
            if ( _instance == null )
            {
                _instance = FindObjectOfType<DefaultCoroutineHost>();
                if ( _instance == null )
                {
                    _instance = new GameObject( "Default Coroutine Host", typeof( DefaultCoroutineHost ) )
                        .GetComponent<DefaultCoroutineHost>();
                }
            }

            return _instance;
        }
    }
}