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

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

Index: pkg/compiler/lib/src/cps_ir/type_propagation.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_propagation.dart b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
index 5784d3ddf1e613cd186ca88c6cc0b17efe3c56a3..e1e727ba8d92292d8f8f7b5cd02789f25a6715c8 100644
--- a/pkg/compiler/lib/src/cps_ir/type_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
@@ -1092,7 +1092,9 @@ class TransformingVisitor extends DeepRecursiveVisitor {
     if (target is! FieldElement) return false;
     // TODO(asgerf): Inlining native fields will make some tests pass for the
     // wrong reason, so for testing reasons avoid inlining them.
-    if (target.isNative || target.isJsInterop) return false;
+    if (backend.isNative(target) || backend.isJsInterop(target)) {
+      return false;
+    }
     Continuation cont = node.continuation.definition;
     if (node.selector.isGetter) {
       GetField get = new GetField(getDartReceiver(node), target);