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 8b27e0178f37c5d9f995758aabc0d2c6db57a545..df107d44e7aa0d427b8c20e0852237c99e5138a2 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_test.dart
@@ -3162,7 +3162,11 @@ 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() {