Report a fatal error on attempt to rename an element declared in SDK.

pkg/analysis_server/test/services/refactoring/rename_unit_member_test.dart

Index: pkg/analysis_server/test/services/refactoring/rename_unit_member_test.dart
diff --git a/pkg/analysis_server/test/services/refactoring/rename_unit_member_test.dart b/pkg/analysis_server/test/services/refactoring/rename_unit_member_test.dart
index 82df4e81d2d0b79e25884b444451594fdd5a8d26..4c799d18f6a228ffe13ee9fedcd1abe42f44bea4 100644
--- a/pkg/analysis_server/test/services/refactoring/rename_unit_member_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/rename_unit_member_test.dart
@@ -224,6 +224,21 @@ class B {
     assertRefactoringStatusOK(status);
   }
 
+  test_checkInitialConditions_inSDK() async {
+    indexTestUnit('''
+main() {
+  String s;
+}
+''');
+    createRenameRefactoringAtString('String s');
+    // check status
+    refactoring.newName = 'NewName';
+    RefactoringStatus status = await refactoring.checkInitialConditions();
+    assertRefactoringStatus(status, RefactoringProblemSeverity.FATAL,
+        expectedMessage:
+            "The class 'String' is defined in the SDK, so cannot be renamed.");
+  }
+
   test_checkNewName_ClassElement() {
     indexTestUnit('''
 class Test {}