Merge CommonElements and BackendHelpers!

pkg/compiler/lib/src/js_emitter/full_emitter/class_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/full_emitter/class_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/full_emitter/class_emitter.dart b/pkg/compiler/lib/src/js_emitter/full_emitter/class_emitter.dart
index 1e41000ef123e93a06de7fd4e628ab7631b752a1..7c19835313df571909722b7cf6e5255e60a794ab 100644
--- a/pkg/compiler/lib/src/js_emitter/full_emitter/class_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/full_emitter/class_emitter.dart
@@ -66,7 +66,7 @@ class ClassEmitter extends CodeEmitterHelper {
     emitRuntimeTypeInformation(cls, builder);
     emitNativeInfo(cls, builder);
 
-    if (classElement == backend.helpers.closureClass) {
+    if (classElement == backend.commonElements.closureClass) {
       // We add a special getter here to allow for tearing off a closure from
       // itself.
       jsAst.Fun function = js('function() { return this; }');