Backport pull request #1529

com.unity.shadergraph/Editor/Drawing/Blackboard/BlackboardFieldPropertyView.cs

 using UnityEngine.Experimental.UIElements;
 using UnityEngine.Experimental.UIElements.StyleSheets;
 using Toggle = UnityEngine.Experimental.UIElements.Toggle;
+#if UNITY_2018_3_OR_NEWER
+using ContextualMenu = UnityEngine.Experimental.UIElements.DropdownMenu;
+#endif
 
 namespace UnityEditor.ShaderGraph.Drawing
 {

com.unity.shadergraph/Editor/Drawing/Inspector/MasterPreviewView.cs

 using UnityEditor.Graphing.Util;
 using UnityEngine.Experimental.UIElements.StyleSheets;
 using Object = UnityEngine.Object;
+#if UNITY_2018_3_OR_NEWER
+using ContextualMenu = UnityEngine.Experimental.UIElements.DropdownMenu;
+#endif
 
 namespace UnityEditor.ShaderGraph.Drawing.Inspector
 {

com.unity.shadergraph/Editor/Drawing/Views/MaterialGraphView.cs

 using Node = UnityEditor.Experimental.UIElements.GraphView.Node;
 using Object = UnityEngine.Object;
 using UnityEditor.Graphs;
+#if UNITY_2018_3_OR_NEWER
+using ContextualMenu = UnityEngine.Experimental.UIElements.DropdownMenu;
+#endif
 
 namespace UnityEditor.ShaderGraph.Drawing
 {

com.unity.shadergraph/Editor/Drawing/Views/MaterialNodeView.cs

 using UnityEngine.Experimental.UIElements.StyleSheets;
 using UnityEngine.Rendering;
 using Node = UnityEditor.Experimental.UIElements.GraphView.Node;
+#if UNITY_2018_3_OR_NEWER
+using ContextualMenu = UnityEngine.Experimental.UIElements.DropdownMenu;
+#endif
 
 namespace UnityEditor.ShaderGraph.Drawing
 {

com.unity.shadergraph/Editor/Util/CompatibilityExtensions.cs

 using System;
 using UnityEngine;
 using UnityEngine.Experimental.UIElements;
+#if UNITY_2018_3_OR_NEWER
+using ContextualMenu = UnityEngine.Experimental.UIElements.DropdownMenu;
+#endif
 
 namespace UnityEditor.ShaderGraph.Drawing
 {