anchor.diff:  
   @reflectiveTest
   class FlutterTest extends AbstractSingleUnitTest {
  -  @override
  -  // TODO(brianwilkerson) Update these tests. I believe that will require
  -  //  updating the mock flutter package.
  -  String? get testPackageLanguageVersion => '2.9';
  -
     Flutter get _flutter => Flutter.instance;
   
     @override
  
positive.code: 
  abstract class Foo extends Widget {
    Widget bar;
  }
  
  void f(Foo foo) {
  
negative.code: 
  abstract class Foo extends Widget {
    Widget bar;
  
    Foo(this.bar);
  }
  
  void f(Foo foo) {
  