Fix #28120, strong mode allows field overrides

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 cb194b0261d713bb450c24e07da64898b70516fb..768bcefeda405208ad0bef9c8f434d7924d3312f 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -2521,12 +2521,6 @@ class ElementAnnotationImpl implements ElementAnnotation {
   static String _REQUIRED_VARIABLE_NAME = "required";
 
   /**
-   * The name of the top-level variable used to mark a member as intended to be
-   * overridden.
-   */
-  static String _VIRTUAL_VARIABLE_NAME = "virtual";
-
-  /**
    * The element representing the field, variable, or constructor being used as
    * an annotation.
    */
@@ -2635,18 +2629,6 @@ class ElementAnnotationImpl implements ElementAnnotation {
           element.library?.name == _META_LIB_NAME;
 
   /**
-   * Return `true` if this annotation marks the associated member as supporting
-   * overrides.
-   *
-   * This is currently used by fields in Strong Mode, as other members are
-   * already virtual-by-default.
-   */
-  bool get isVirtual =>
-      element is PropertyAccessorElement &&
-      element.name == _VIRTUAL_VARIABLE_NAME &&
-      element.library?.name == _META_LIB_NAME;
-
-  /**
    * Get the library containing this annotation.
    */
   Source get librarySource => compilationUnit.librarySource;
@@ -4273,14 +4255,7 @@ class FieldElementImpl extends PropertyInducingElementImpl
   }
 
   @override
-  bool get isVirtual {
-    for (ElementAnnotationImpl annotation in metadata) {
-      if (annotation.isVirtual) {
-        return true;
-      }
-    }
-    return false;
-  }
+  bool get isVirtual => true;
 
   @override
   ElementKind get kind => ElementKind.FIELD;