Add NativeEnqueuer to work with the Enqueuer.

lib/compiler/implementation/js_backend/backend.dart

Index: lib/compiler/implementation/js_backend/backend.dart
diff --git a/lib/compiler/implementation/js_backend/backend.dart b/lib/compiler/implementation/js_backend/backend.dart
index 9f79fcc96ecaba6ca020090308cef0e24c32fab0..e507c221aada6f1c344df5bfab779d1f1e83ed19 100644
--- a/lib/compiler/implementation/js_backend/backend.dart
+++ b/lib/compiler/implementation/js_backend/backend.dart
@@ -745,10 +745,17 @@ class JavaScriptBackend extends Backend {
     invalidateAfterCodegen.clear();
   }
 
-  void processNativeClasses(Enqueuer world,
-                            Collection<LibraryElement> libraries) {
-    native.processNativeClasses(world, emitter, libraries);
-  }
+
+  NativeEnqueuer nativeResolutionEnqueuer(Enqueuer world) =>
+      new native.NativeResolutionEnqueuer(world, compiler);
+
+  NativeEnqueuer nativeCodegenEnqueuer(Enqueuer world) =>
+      new native.NativeCodegenEnqueuer(world, compiler, emitter);
+
+  //void processNativeClasses(Enqueuer world,
+  //                          Collection<LibraryElement> libraries) {
+  //  native.processNativeClasses(world, emitter, libraries);
+  //}
 
   void assembleProgram() {
     emitter.assembleProgram();