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

pkg/compiler/lib/src/js_emitter/program_builder/collector.dart

Index: pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
diff --git a/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart b/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
index 62ba314a57e9892d52b4144f0426413e403314fb..69babce0b9209603bc396822d64e2ba45d90f64e 100644
--- a/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
+++ b/pkg/compiler/lib/src/js_emitter/program_builder/collector.dart
@@ -236,7 +236,7 @@ class Collector {
     List<ClassElement> sortedClasses = Elements.sortedByPosition(neededClasses);
 
     for (ClassElement element in sortedClasses) {
-      if (Elements.isNativeOrExtendsNative(element) &&
+      if (backend.isNativeOrExtendsNative(element) &&
           !classesOnlyNeededForRti.contains(element)) {
         // For now, native classes and related classes cannot be deferred.
         nativeClassesAndSubclasses.add(element);