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

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

 // Copyright (c) 2015, 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.
 
 part of dart2js.js_emitter.program_builder;
 
 /**
  * [member] is a field (instance, static, or top level).
  *
  * [name] is the field name that the [Namer] has picked for this field's
@@ skipping 62 matching lines @@
     // inheritance purposes, but we can simplify its JavaScript constructor.
     bool isInstantiated =
         compiler.codegenWorld.directlyInstantiatedClasses.contains(element);
 
     void visitField(Element holder, FieldElement field) {
       assert(invariant(element, field.isDeclaration));
 
       // Keep track of whether or not we're dealing with a field mixin
       // into a native class.
       bool isMixinNativeField =
-          isClass && element.isNative && holder.isMixinApplication;
+          isClass && backend.isNative(element) && holder.isMixinApplication;
 
       // See if we can dynamically create getters and setters.
       // We can only generate getters and setters for [element] since
       // the fields of super classes could be overwritten with getters or
       // setters.
       bool needsGetter = false;
       bool needsSetter = false;
       if (isLibrary || isMixinNativeField || holder == element) {
         needsGetter = fieldNeedsGetter(field);
         needsSetter = fieldNeedsSetter(field);
       }
 
-      if ((isInstantiated && !holder.isNative)
+      if ((isInstantiated && !backend.isNative(holder))
           || needsGetter
           || needsSetter) {
         js.Name accessorName = namer.fieldAccessorName(field);
         js.Name fieldName = namer.fieldPropertyName(field);
         bool needsCheckedSetter = false;
         if (compiler.enableTypeAssertions
             && needsSetter
             && !canAvoidGeneratedCheckedSetter(field)) {
           needsCheckedSetter = true;
           needsSetter = false;
@@ skipping 54 matching lines @@
       field is ClosureFieldElement;
   }
 
   bool canAvoidGeneratedCheckedSetter(VariableElement member) {
     // We never generate accessors for top-level/static fields.
     if (!member.isInstanceMember) return true;
     DartType type = member.type;
     return type.treatAsDynamic || (type.element == compiler.objectClass);
   }
 }