Merge pull request #2013 from umbraco/temp-U4-10046

U4-10046 Stop resolving TreeController from the PluginManager for eve…

src/Umbraco.Web/Editors/BackOfficeController.cs

@@ -718,11 +718,19 @@ namespace Umbraco.Web.Editors
 
             return app;
         }
-
+
+        /// <summary>
+        /// A lazy reference to all tree controller types
+        /// </summary>
+        /// <remarks>
+        /// We are doing this because if we constantly resolve the tree controller types from the PluginManager it will re-scan and also re-log that
+        /// it's resolving which is unecessary and annoying. 
+        /// </remarks>
+        private static readonly Lazy<IEnumerable<Type>> TreeControllerTypes = new Lazy<IEnumerable<Type>>(() => PluginManager.Current.ResolveAttributedTreeControllers().ToArray());
 
         private IEnumerable<Dictionary<string, string>> GetTreePluginsMetaData()
         {
-            var treeTypes = PluginManager.Current.ResolveAttributedTreeControllers();
+            var treeTypes = TreeControllerTypes.Value;
             //get all plugin trees with their attributes
             var treesWithAttributes = treeTypes.Select(x => new
             {