Annotate native methods.

pkg/front_end/lib/src/fasta/builder/library_builder.dart

Index: pkg/front_end/lib/src/fasta/builder/library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/builder/library_builder.dart b/pkg/front_end/lib/src/fasta/builder/library_builder.dart
index f3932b3be29e07204bec8afaac191b61d360ced9..3cb2ea165246eb17f22b6e366ae0b058ad1defe0 100644
--- a/pkg/front_end/lib/src/fasta/builder/library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/library_builder.dart
@@ -72,6 +72,8 @@ abstract class LibraryBuilder<T extends TypeBuilder, R> extends Builder {
 
   int finishStaticInvocations() => 0;
 
+  int finishNativeMethods() => 0;
+
   /// Looks up [constructorName] in the class named [className]. It's an error
   /// if no such class is exported by this library, or if the class doesn't
   /// have a matching constructor (or factory).