Add an UNUSED_SHOWN_NAMES hint to the analyzer

pkg/analyzer/test/src/summary/resynthesize_test.dart

Index: pkg/analyzer/test/src/summary/resynthesize_test.dart
diff --git a/pkg/analyzer/test/src/summary/resynthesize_test.dart b/pkg/analyzer/test/src/summary/resynthesize_test.dart
index aa938d7571f3ecbd6cabade9e5b2fe0bc633f8d3..c523de8f2518817a41abe420bbd0008c04512674 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_test.dart
@@ -3142,7 +3142,11 @@ get x => null;''');
 
   test_import_show() {
     addLibrary('dart:async');
-    checkLibrary('import "dart:async" show Future, Stream; Future f;');
+    checkLibrary('''
+import "dart:async" show Future, Stream;
+Future f;
+Stream s;
+''');
   }
 
   test_imports() {