Log time elapsed when compiling shaders

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/PreviewManager.cs

 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;
 using UnityEditor.Graphing;
 using UnityEditor.ShaderGraph;
 using UnityEngine.Rendering;
+using Debug = UnityEngine.Debug;
 using Object = UnityEngine.Object;
 
 namespace UnityEditor.ShaderGraph.Drawing
 
                 try
                 {
+                    var sw = new Stopwatch();
+                    sw.Start();
                     var i = 0;
                     EditorUtility.DisplayProgressBar("Shader Graph", string.Format("Compiling preview shaders ({0}/{1})", i, count), 0f);
                     foreach (var node in masterNodes)
                         i++;
                         EditorUtility.DisplayProgressBar("Shader Graph", string.Format("Compiling preview shaders ({0}/{1})", i, count), 0f);
                     }
+                    sw.Stop();
+                    Debug.LogFormat("Compiled preview shaders in {0} seconds", sw.Elapsed.TotalSeconds);
                 }
                 finally
                 {
                 }
                 m_PreviewProperties.Clear();
             }
-
 
             foreach (var nodeGuid in m_DirtyPreviews)
             {