[web] Add test for Image.network (#22256)

e2etests/web/regular_integration_tests/lib/image_loading_main.dart

@@ -6,8 +6,9 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
 void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
   const MethodChannel channel =
-  OptionalMethodChannel('flutter/web_test_e2e', JSONMethodCodec());
+      OptionalMethodChannel('flutter/web_test_e2e', JSONMethodCodec());
   await channel.invokeMethod<void>(
     'setDevicePixelRatio',
     '1.5',
@@ -26,7 +27,10 @@ class MyAppState extends State<MyApp> {
     return MaterialApp(
         key: const Key('mainapp'),
         title: 'Integration Test App',
-        home: Image.asset('assets/images/sample_image1.png')
+        home: Column(children: <Widget>[
+          Image.asset('assets/images/sample_image1.png'),
+          Image.network('assets/images/sample_image1.png'),
+      ])
     );
   }
 }

e2etests/web/regular_integration_tests/test_driver/image_loading_integration.dart

@@ -15,10 +15,12 @@ void main() {
           (WidgetTester tester) async {
     app.main();
     await tester.pumpAndSettle();
-    final html.ImageElement imageElement = html.querySelector('img') as html.ImageElement;
-    expect(imageElement.naturalWidth, 1.5 * 100);
-    expect(imageElement.naturalHeight, 1.5 * 100);
-    expect(imageElement.width, 100);
-    expect(imageElement.height, 100);
+    final List<html.ImageElement> imageElements = html.querySelectorAll('img');
+    expect(imageElements.length, 2);
+    expect(imageElements[0].naturalWidth, 1.5 * 100);
+    expect(imageElements[0].naturalHeight, 1.5 * 100);
+    expect(imageElements[0].width, 100);
+    expect(imageElements[0].height, 100);
+    expect(imageElements[1].width, isNot(0));
   });
 }