Issue 25733. Built-in itentifiers are not permitted as prefixes.

pkg/analyzer/test/generated/compile_time_error_code_test.dart

Index: pkg/analyzer/test/generated/compile_time_error_code_test.dart
diff --git a/pkg/analyzer/test/generated/compile_time_error_code_test.dart b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
index 3c95c9da539709978d5e16b8590aa375545af459..a8b21c9894860280119ed29c2eee7ebdb869c521 100644
--- a/pkg/analyzer/test/generated/compile_time_error_code_test.dart
+++ b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
@@ -624,6 +624,16 @@ class as = A with B;''');
     verify([source]);
   }
 
+  test_builtInIdentifierAsPrefixName() async {
+    Source source = addSource("import 'dart:async' as abstract;");
+    await computeAnalysisResult(source);
+    assertErrors(source, [
+      CompileTimeErrorCode.BUILT_IN_IDENTIFIER_AS_PREFIX_NAME,
+      HintCode.UNUSED_IMPORT
+    ]);
+    verify([source]);
+  }
+
   test_builtInIdentifierAsType_formalParameter_field() async {
     Source source = addSource(r'''
 class A {