Store actual Reference(s) for additional exports.

pkg/kernel/lib/binary/ast_to_binary.dart

Index: pkg/kernel/lib/binary/ast_to_binary.dart
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index 23eaefd97854a97872b79e9ddfc035fc57c11b1f..ec8f413fd23cce9d87662698619e458173f62d5e 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -312,6 +312,7 @@ class BinaryPrinter extends Visitor {
     writeUriReference(node.fileUri ?? '');
     writeAnnotationList(node.annotations);
     writeLibraryDependencies(node);
+    writeAdditionalExports(node);
     writeLibraryParts(node);
     writeNodeList(node.typedefs);
     writeNodeList(node.classes);
@@ -331,6 +332,13 @@ class BinaryPrinter extends Visitor {
     }
   }
 
+  void writeAdditionalExports(Library library) {
+    writeUInt30(library.additionalExports.length);
+    for (Reference ref in library.additionalExports) {
+      writeReference(ref);
+    }
+  }
+
   void writeLibraryDependency(LibraryDependency node) {
     writeByte(node.flags);
     writeNodeList(node.annotations);