dart2js: don't pass the supername to visitFields.

pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart

Index: pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
index 80a6e7402377046c8c993bf782297cc4238b25b6..c7a2fed40fa9a52e53a127f0073a26b561201e35 100644
--- a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
@@ -1322,7 +1322,7 @@ class OldEmitter implements Emitter {
     for (LibraryElement element in libraries) {
       LibraryElement library = element;
       ClassBuilder builder = new ClassBuilder(library, namer);
-      if (classEmitter.emitFields(library, builder, null, emitStatics: true)) {
+      if (classEmitter.emitFields(library, builder, emitStatics: true)) {
         jsAst.ObjectInitializer initializer = builder.toObjectInitializer();
         compiler.dumpInfoTask.registerElementAst(builder.element, initializer);
         getElementDescriptor(library).properties.addAll(initializer.properties);