Serialize also canonical names of 'interfaceTargetReference'.

pkg/kernel/lib/binary/limited_ast_to_binary.dart

Index: pkg/kernel/lib/binary/limited_ast_to_binary.dart
diff --git a/pkg/kernel/lib/binary/limited_ast_to_binary.dart b/pkg/kernel/lib/binary/limited_ast_to_binary.dart
index ba17cab47d5e21535ae917c2c74f2bbe67aeb952..355c35c9c9eb22c89971c342d790b6e6dd38a82f 100644
--- a/pkg/kernel/lib/binary/limited_ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/limited_ast_to_binary.dart
@@ -65,6 +65,10 @@ class ReferencesStringIndexer extends StringIndexer {
     _handleReferencedName(node.canonicalName);
   }
 
+  visitInterfaceTargetReference(Reference reference) {
+    _handleReferencedName(reference?.canonicalName);
+  }
+
   void _handleReferencedName(CanonicalName name) {
     if (name == null || name.parent == null) return;
     _handleReferencedName(name.parent);