revert deleted test

packages/webview_flutter/webview_flutter_web/test/webview_flutter_web_test.dart

@@ -55,6 +55,19 @@ void main() {
       verify(mockElement.src = 'test url');
     });
 
+    test('loadHtmlString loads html into iframe', () {
+      // Setup
+      final MockIFrameElement mockElement = MockIFrameElement();
+      final WebWebViewPlatformController controller =
+          WebWebViewPlatformController(
+        mockElement,
+      );
+      // Run
+      controller.loadHtmlString('test html');
+      // Verify
+      verify(mockElement.src = 'data:text/html,${Uri.encodeFull('test html')}');
+    });
+
     test('loadHtmlString escapes "#" correctly', () {
       // Setup
       final MockIFrameElement mockElement = MockIFrameElement();