**Function: - Add menu DoC/Start with first game scene to Unity3D editor main menus. - The menu starts playing your game from the specified scene and brings you back to the scene you were editting when stop playing

StartWithSpecificScene.cs

using UnityEngine;
using System.Collections;
using UnityEditor;

/* by FVS - Ha Luan */

public class StartWithSpecificScene : Editor
{
    const string settingKey = "FVSHaluanStartWithSpecificScene";
    const string firstScenePath = "Assets/Scenes/Login.unity";
    static string sceneBeforeStart = "";
    static bool isInited = false;

    [MenuItem("DoC/Start with first game scene")]
    static void StartGame()
    {
        if (!isInited)
        {
            Init();
        }

        if (EditorApplication.isPlaying)
        {
            EditorApplication.isPlaying = false;
            return;
        }

        sceneBeforeStart = EditorApplication.currentScene;
        EditorApplication.SaveCurrentSceneIfUserWantsTo();
        EditorApplication.OpenScene(firstScenePath);
        SaveScenePath();
        EditorApplication.isPlaying = true;
    }

    [InitializeOnLoadMethod]
    static void Init()
    {
        EditorApplication.playmodeStateChanged += OnUnityPlayModeChanged;
        isInited = true;
    }

    static void OnStopGame()
    {
        LoadScenePath();
        if (!string.IsNullOrEmpty(sceneBeforeStart))
        {
            EditorApplication.OpenScene(sceneBeforeStart);
            sceneBeforeStart = "";
        }
    }

    static void SaveScenePath()
    {
        EditorPrefs.SetString(settingKey, sceneBeforeStart);        
    }

    static void LoadScenePath()
    {
        sceneBeforeStart = EditorPrefs.GetString(settingKey, "");
    }

    static void OnUnityPlayModeChanged()
    {
        if (EditorApplication.isPlaying && !EditorApplication.isPlayingOrWillChangePlaymode)
        {
            OnStopGame();
        }
    }
}