Ensure resolution of metadata on parts for serialization.

tests/compiler/dart2js/serialization/test_data.dart

Index: tests/compiler/dart2js/serialization/test_data.dart
diff --git a/tests/compiler/dart2js/serialization/test_data.dart b/tests/compiler/dart2js/serialization/test_data.dart
index cfb2d08e70dbfd9d9ddd2b095a70f0943c64d08a..9038877f5892e9dac54446ff2ab449b58dce82e6 100644
--- a/tests/compiler/dart2js/serialization/test_data.dart
+++ b/tests/compiler/dart2js/serialization/test_data.dart
@@ -718,6 +718,36 @@ export 'main.dart';
 main() {}
 '''}),
 
+  const Test('Metadata on part tags', const {},
+      preserializedSourceFiles: const {
+        'main.dart': '''
+library main;
+
+@deprecated
+part 'a.dart';
+
+main() {}
+'''},
+      unserializedSourceFiles: const {
+        'a.dart': '''
+part of main;
+'''}),
+
+  const Test('Metadata on part-of tags', const {},
+      preserializedSourceFiles: const {
+        'main.dart': '''
+library main;
+
+part 'a.dart';
+
+main() {}
+'''},
+      unserializedSourceFiles: const {
+        'a.dart': '''
+@deprecated
+part of main;
+'''}),
+
   const Test('Ambiguous elements', const {},
       preserializedSourceFiles: const {
         'main.dart': '''