Store actual Reference(s) for additional exports.

pkg/kernel/lib/ast.dart

Index: pkg/kernel/lib/ast.dart
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index d404cc92cbdb2feba735b4c4fd99f50d8c1396f5..97c7976252c21adf73de38a83077ac62e97c0337 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -269,6 +269,11 @@ class Library extends NamedNode implements Comparable<Library> {
   String name;
   final List<Expression> annotations;
   final List<LibraryDependency> dependencies;
+
+  /// Additional nodes exported by this library with `export` directives and
+  /// not hidden by local declarations.
+  final List<Reference> additionalExports = <Reference>[];
+
   @informative
   final List<LibraryPart> parts;
   final List<Typedef> typedefs;