When attached to a Camera, shows that cameras frustum culling in the scene view

PreviewCulling.cs

using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
#endif
using System.Collections;

[ExecuteInEditMode]
public class PreviewCulling : MonoBehaviour {
	
	#if UNITY_EDITOR
	
	static Camera sceneReferenceCamera;
	
	Vector3 pos;
	Quaternion rot;
	float near;
	float far;
	
	new Camera camera;

    bool IsSceneViewCamera(Camera cam)
    {
        Camera[] sceneCameras = SceneView.GetAllSceneCameras();
        for (int i = 0; i < sceneCameras.Length; i++){
            if (cam == sceneCameras[i]) { return true; }
        }
        return false;
    }
	
	void OnEnable() {
        camera = GetComponent<Camera>();
        if (camera && !IsSceneViewCamera(camera)) {
            sceneReferenceCamera = camera;
            UpdateSceneCameras();
        }
	}
	
	void OnDisable() {
        if (camera && sceneReferenceCamera == camera) {
			CleanSceneCameras();
			sceneReferenceCamera = null;
		}
	}
	
	private void UpdateSceneCameras() {
        //add a PreviewCulling script to the scene camera if not done already
        Camera[] sceneCameras = SceneView.GetAllSceneCameras();
        for (int i = 0; i < sceneCameras.Length; i++) {
            if (!sceneCameras[i].GetComponent<PreviewCulling>()) {
                sceneCameras[i].gameObject.AddComponent<PreviewCulling>();
            }
        }
	}
	
	void CleanSceneCameras() {
        Camera[] sceneCameras = SceneView.GetAllSceneCameras();
        for (int i = 0; i < sceneCameras.Length; i++) {
            PreviewCulling pc = sceneCameras[i].GetComponent<PreviewCulling>();
            if (pc) {
                DestroyImmediate(pc);
            }
        }
	}

    void OnPreCull() {
        //if the scene camera is about to cull, save current transform values and copy from the reference camera
        if (camera && sceneReferenceCamera && IsSceneViewCamera(camera)) { 
			pos  = transform.position;
			rot  = transform.rotation;
			near = camera.nearClipPlane;
			far  = camera.farClipPlane;
            camera.projectionMatrix = sceneReferenceCamera.projectionMatrix;
            camera.transform.position = sceneReferenceCamera.transform.position;
            camera.transform.rotation = sceneReferenceCamera.transform.rotation;
            camera.nearClipPlane = sceneReferenceCamera.nearClipPlane;
            camera.farClipPlane = sceneReferenceCamera.farClipPlane;
		}
	}
	
	void OnPreRender() {
        //if the scene camera is about to render reset its transform to saved values
        if (camera && IsSceneViewCamera(camera)) {
			transform.position = pos;
			transform.rotation = rot;
            camera.nearClipPlane = near;
            camera.farClipPlane = far;
            camera.ResetProjectionMatrix();
		}
	}
	#endif
}