add network request sample

Samples/UIWidgetsSamples_2019_4/Assets/MaterialSample/NetWorkImageSample.cs

+using System.Collections;
+using System.Collections.Generic;
+using Unity.UIWidgets.engine2;
+using Unity.UIWidgets.material;
+using Unity.UIWidgets.painting;
+using Unity.UIWidgets.widgets;
+using UnityEngine;
+
+namespace UIWidgetsSample
+{
+    public class NetWorkImageSample : UIWidgetsPanel
+    {
+        protected override void main()
+        {
+            ui_.runApp(new MaterialApp(
+                showPerformanceOverlay: false,
+                home: new NetWorkeImageWidget()));
+        }
+
+        class NetWorkeImageWidget : StatelessWidget { 
+                public override Widget build(BuildContext context) {
+                var title = "NetWork Image";
+
+                return new MaterialApp(
+                    title: title,
+                    home: new Scaffold(
+                        appBar: new AppBar(
+                            title: new Text(title)
+                        ),
+                        body: Image.network("https://picsum.photos/250?image=2")
+                    )
+                );
+            }
+        }
+    }
+
+}
+
+
+