create background editor process

TestWindow.cs

using UnityEngine;
using UnityEditor;
using System.Collections;

public class TestWindow : EditorWindow
{
	[MenuItem("Window/Test")]
	public static void Init ()
	{
		EditorWindow.GetWindow (typeof(TestWindow));
	}
	void OnGUI ()
	{
		if (GUILayout.Button ("Go")) {
			EditorApplication.update += TestProcess;
		}
	}
	
	int count = 0;
	void TestProcess ()
	{
		Debug.Log (count++);
		if (count > 100) {
			count = 0;
			EditorApplication.update -= TestProcess;
		}
	}
}