[InitializeOnLoad]
[ExecuteInEditMode]
public partial class CSimulateEnv : MonoBehaviour
{
    static CSimulateEnv()
    {
       ClearLog();
    }
}

using System.Reflection;
using UnityEngine;

public class ClearTest : MonoBehaviour
{
    // Use this for initialization
    void Start()
    {
        ClearLog();
    }

    void OnGUI()
    {
        if (GUILayout.Button(" clear "))
        {
            ClearLog();
        }
    }

    public void ClearLog()
    {
        var assembly = Assembly.GetAssembly(typeof(UnityEditor.ActiveEditorTracker));
        var type = assembly.GetType("UnityEditorInternal.LogEntries");
        var method = type.GetMethod("Clear");
        method.Invoke(new object(), null);
    }
}