Move native and js interop properties from the element model to the JS backend

pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
index 3f69cd04c4958acf26b6e392babe5c9f61ab47bb..934919d4cb8041c67e7c89e5d3648f76f956b663 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
@@ -2073,8 +2073,8 @@ class IrBuilder {
   /// `fixedBackendName`, passing all parameters as arguments.  The target can
   /// be the JavaScript implementation of a function, getter, or setter.
   void buildRedirectingNativeFunctionBody(FunctionElement function,
+                                          String name,
                                           SourceInformation source) {
-    String name = function.fixedBackendName;
     List<ir.Primitive> arguments = <ir.Primitive>[];
     NativeBehavior behavior = new NativeBehavior();
     behavior.sideEffects.setAllSideEffects();