Merge CommonElements and BackendHelpers!

pkg/compiler/lib/src/native/ssa.dart

Index: pkg/compiler/lib/src/native/ssa.dart
diff --git a/pkg/compiler/lib/src/native/ssa.dart b/pkg/compiler/lib/src/native/ssa.dart
index ca40035cb708a260a983792f57dd5a70d43ddcce..200b98b6dab6e698132cc826491036e425c16cee 100644
--- a/pkg/compiler/lib/src/native/ssa.dart
+++ b/pkg/compiler/lib/src/native/ssa.dart
@@ -28,7 +28,7 @@ void handleSsaNative(SsaBuilder builder, Expression nativeBody) {
         builder.graph.addConstant(arityConstant, builder.closedWorld);
     // TODO(ngeoffray): For static methods, we could pass a method with a
     // defined arity.
-    MethodElement helper = builder.helpers.closureConverter;
+    MethodElement helper = builder.commonElements.closureConverter;
     builder.pushInvokeStatic(nativeBody, helper, [local, arity]);
     HInstruction closure = builder.pop();
     return closure;