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

pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart

 // Copyright (c) 2014, 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.js_emitter.full_emitter;
 
 import 'dart:convert';
 import 'dart:collection' show HashMap;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
@@ skipping 1815 matching lines @@
       return '''
 
 //# sourceMappingURL=$sourceMapFileName
 ''';
     }
     return '';
   }
 
   ClassBuilder getElementDescriptor(Element element, Fragment fragment) {
     Element owner = element.library;
-    if (!element.isLibrary && !element.isTopLevel && !element.isNative) {
+    if (!element.isLibrary &&
+        !element.isTopLevel &&
+        !backend.isNative(element)) {
       // For static (not top level) elements, record their code in a buffer
       // specific to the class. For now, not supported for native classes and
       // native elements.
       ClassElement cls =
           element.enclosingClassOrCompilationUnit.declaration;
       if (compiler.codegenWorld.directlyInstantiatedClasses.contains(cls) &&
-          !cls.isNative &&
+          !backend.isNative(cls) &&
           compiler.deferredLoadTask.outputUnitForElement(element) ==
               compiler.deferredLoadTask.outputUnitForElement(cls)) {
         owner = cls;
       }
     }
     if (owner == null) {
       reporter.internalError(element, 'Owner is null.');
     }
     return elementDescriptors
         .putIfAbsent(fragment, () => new Map<Element, ClassBuilder>())
@@ skipping 266 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }