Compute export namespaces for DILL libraries.

pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart

Index: pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart b/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart
index 76be7d3b110afaf66bc2a981da6faa3001a0588d..0e6f177afa941bcbb235d9907b4e9a1071e25018 100644
--- a/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/dill/dill_library_builder.dart
@@ -111,10 +111,6 @@ class DillLibraryBuilder extends LibraryBuilder<KernelTypeBuilder, Library> {
     addBuilder(typedef.name, typedefBuilder, typedef.fileOffset);
   }
 
-  bool addToExportScope(String name, Builder member) {
-    return internalError("Not implemented yet.");
-  }
-
   @override
   void addToScope(String name, Builder member, int charOffset, bool isImport) {
     internalError("Not implemented yet.");