Add SemanticVisitor to dart2js.

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 0ba3b3d6a37b416e9cb01aca8e8bedd35462854e..226e5f540422f725b35767939fde79b06ca44758 100644
--- a/pkg/compiler/lib/src/use_unused_api.dart
+++ b/pkg/compiler/lib/src/use_unused_api.dart
@@ -28,6 +28,7 @@ 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 'js_emitter/program_builder.dart' as program_builder;
+import 'resolution/semantic_visitor.dart' as semantic_visitor;
 import 'source_file_provider.dart' as source_file_provider;
 import 'ssa/ssa.dart' as ssa;
 import 'tree/tree.dart' as tree;
@@ -69,6 +70,7 @@ void main(List<String> arguments) {
   useCodeEmitterTask(null);
   useScript(null);
   useProgramBuilder(null);
+  useSemanticVisitor();
 }
 
 useApi() {
@@ -291,3 +293,8 @@ useProgramBuilder(program_builder.ProgramBuilder builder) {
   builder.buildMethodHackForIncrementalCompilation(null);
   builder.buildFieldsHackForIncrementalCompilation(null);
 }
+
+useSemanticVisitor() {
+  new semantic_visitor.BulkVisitor().apply(null, null);
+  new semantic_visitor.TraversalVisitor(null).apply(null, null);
+}