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

pkg/compiler/lib/src/world.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.world;
 
 import 'closure.dart' show
     SynthesizedCallMethodElementX;
 import 'common.dart';
 import 'common/backend_api.dart' show
@@ skipping 592 matching lines @@
   void addFunctionCalledInLoop(Element element) {
     functionsCalledInLoop.add(element.declaration);
   }
 
   bool isCalledInLoop(Element element) {
     return functionsCalledInLoop.contains(element.declaration);
   }
 
   bool fieldNeverChanges(Element element) {
     if (!element.isField) return false;
-    if (element.isNative) {
+    if (backend.isNative(element)) {
       // Some native fields are views of data that may be changed by operations.
       // E.g. node.firstChild depends on parentNode.removeBefore(n1, n2).
       // TODO(sra): Refine the effect classification so that native effects are
       // distinct from ordinary Dart effects.
       return false;
     }
 
     return element.isFinal
         || element.isConst
         || (element.isInstanceMember
@@ skipping 68 matching lines @@
     // function expressions's element.
     // TODO(herhut): Generate classes for function expressions earlier.
     if (element is SynthesizedCallMethodElementX) {
       return getMightBePassedToApply(element.expression);
     }
     return functionsThatMightBePassedToApply.contains(element);
   }
 
   bool get hasClosedWorldAssumption => !compiler.hasIncrementalSupport;
 }