Elements. Tweak MetadataResolutionTest.

Change-Id: I9089d646ab47c061d2d8ea0e38a7d1e8a82540e2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/400340
Reviewed-by: Phil Quitslund <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/test/src/dart/resolution/metadata_test.dart

@@ -268,7 +268,7 @@ Annotation
 ''');
 
     var localVariable = findElement2.localVar('x');
-    var annotationOnElement = localVariable.firstAnnotation;
+    var annotationOnElement = localVariable.metadata2.annotations.first;
     _assertElementAnnotationValueText(annotationOnElement, '''
 A
   a: int 3
@@ -1485,8 +1485,8 @@ import 'a.dart';
 void f(C c) {}
 ''');
 
-    var classC = findNode.namedType('C c').element2!;
-    var annotation = classC.firstAnnotation;
+    var classC = findNode.namedType('C c').element2 as ClassElement2;
+    var annotation = classC.metadata2.annotations.first;
     _assertElementAnnotationValueText(annotation, r'''
 B
   a: A
@@ -1515,8 +1515,8 @@ import 'b.dart';
 void f(B b) {}
 ''');
 
-    var classB = findNode.namedType('B b').element2!;
-    var annotation = classB.firstAnnotation;
+    var classB = findNode.namedType('B b').element2! as ClassElement2;
+    var annotation = classB.metadata2.annotations.first;
     _assertElementAnnotationValueText(annotation, r'''
 A
   f: int 42
@@ -1544,8 +1544,8 @@ import 'b.dart';
 void f(B b) {}
 ''');
 
-    var classB = findNode.namedType('B b').element2!;
-    var annotation = classB.firstAnnotation;
+    var classB = findNode.namedType('B b').element2 as ClassElement2;
+    var annotation = classB.metadata2.annotations.first;
     _assertElementAnnotationValueText(annotation, r'''
 A
   f: int 42
@@ -2671,8 +2671,3 @@ int 42
     assertDartObjectText(value, expected);
   }
 }
-
-extension on Element2 {
-  ElementAnnotation get firstAnnotation =>
-      (this as Annotatable).metadata2.annotations.first;
-}