fix #28008, fix #28009 implement FutureOr<T>

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 308501bdca3d0589f6582d1b9c1507eefff8cf18..a9d85a0222baf4efdef6c0dfbd8420e51a737ae5 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -7886,6 +7886,8 @@ abstract class PropertyInducingElementImpl
  * The context in which elements are resynthesized.
  */
 abstract class ResynthesizerContext {
+  bool get isStrongMode;
+
   /**
    * Build [ElementAnnotationImpl] for the given [UnlinkedExpr].
    */