Use the unused [assembleCode].

pkg/compiler/lib/src/use_unused_api.dart

Index: pkg/compiler/lib/src/use_unused_api.dart
diff --git a/pkg/compiler/lib/src/use_unused_api.dart b/pkg/compiler/lib/src/use_unused_api.dart
index 2713e0df0f3f931676b57cd2a0de4639e5917e44..e7506c17987b843970ec04e8465577b9c704550a 100644
--- a/pkg/compiler/lib/src/use_unused_api.dart
+++ b/pkg/compiler/lib/src/use_unused_api.dart
@@ -25,6 +25,7 @@ import 'inferrer/concrete_types_inferrer.dart' as concrete_types_inferrer;
 import 'inferrer/type_graph_inferrer.dart' as type_graph_inferrer;
 import 'io/code_output.dart' as io;
 import 'js/js.dart' as js;
+import 'js_backend/js_backend.dart' as js_backend;
 import 'js_emitter/js_emitter.dart' as js_emitter;
 import 'source_file_provider.dart' as source_file_provider;
 import 'ssa/ssa.dart' as ssa;
@@ -53,6 +54,7 @@ void main(List<String> arguments) {
   useJs(new js.Blob(null));
   useJs(new js.NamedFunction(null, null));
   useJs(new js.ArrayHole());
+  useJsBackend(null);
   useConcreteTypesInferrer(null);
   useColor();
   useFilenames();
@@ -170,6 +172,10 @@ useJs(js.Node node) {
   node.asVariableUse();
 }
 
+useJsBackend(js_backend.JavaScriptBackend backend) {
+  backend.assembleCode(null);
+}
+
 useConcreteTypesInferrer(concrete_types_inferrer.ConcreteTypesInferrer c) {
   c.debug();
 }