Use concrete factory constructor for DomXMLHttpRequest (#115094)

This code should be calling the factory method, not the synthetic
constructor.

packages/flutter/lib/src/painting/_network_image_web.dart

@@ -18,7 +18,7 @@ typedef HttpRequestFactory = DomXMLHttpRequest Function();
 
 /// Default HTTP client.
 DomXMLHttpRequest _httpClient() {
-  return DomXMLHttpRequest();
+  return createDomXMLHttpRequest();
 }
 
 /// Creates an overridable factory function.