fix some sample errors

Author: zhuxingwei

Tests/Editor/Menu.cs

@@ -32,6 +32,8 @@ public static void renderWidgets() {
             EditorWindow.GetWindow(typeof(Widgets));
         }
 
+        //These samples are not available after Unity2019.1
+        /*
         [MenuItem("UIWidgetsTests/Show SceneViewTests")]
         public static void showSceneView() {
             SceneViewTests.show();
@@ -40,6 +42,6 @@ public static void showSceneView() {
         [MenuItem("UIWidgetsTests/Hide SceneViewTests")]
         public static void hideSceneView() {
             SceneViewTests.hide();
-        }
+        }*/
     }
 }

Tests/Editor/MouseHover.cs

@@ -24,12 +24,16 @@ public static Widget createRow(bool canHover = true, bool nest = false) {
                     result, "inner");
             }
 
+            //WARNING: nested MouseTracker is not supported by the current implementation that ported from flutter
+            //refer to this issue https://github.com/flutter/flutter/issues/28407 and wait Google guys fixing it
+            /*
             if (nest) {
                 result = new Container(child: result, padding: EdgeInsets.all(40),
                     color: Color.fromARGB(255, 255, 0, 0));
                 result = new HoverTrackWidget(null,
                     result, "outer");
             }
+            */
 
             return result;
         }