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 970a7e64a5a97a7a4b07fbb4db1c66aec286544c..0e2cad7752ef948eda5cc4be00fe73f55c577ee0 100644
--- a/pkg/compiler/lib/src/native/ssa.dart
+++ b/pkg/compiler/lib/src/native/ssa.dart
@@ -33,7 +33,7 @@ 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 = backend.helpers.closureConverter;
+    MethodElement helper = backend.commonElements.closureConverter;
     builder.pushInvokeStatic(nativeBody, helper, [local, arity]);
     HInstruction closure = builder.pop();
     return closure;