Support user generated custom native JS classes.

pkg/compiler/lib/src/elements/modelx.dart

 // Copyright (c) 2013, 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 elements.modelx;
 
 import '../compiler.dart' show
     Compiler;
 import '../constants/constant_constructors.dart';
 import '../constants/constructors.dart';
@@ skipping 207 matching lines @@
           ? enclosingElement.name
           : '${enclosingElement.kind}?';
       return '$kind($holderName#${nameText})';
     } else {
       return '$kind(${nameText})';
     }
   }
 
   String _fixedBackendName = null;
   bool _isNative = false;
-  bool get isNative => _isNative;
+  bool isJsInterop = false;
+  bool get isNative => _isNative || isJsInterop;
   bool get hasFixedBackendName => _fixedBackendName != null;
   String get fixedBackendName => _fixedBackendName;
   // Marks this element as a native element.
   void setNative(String name) {
     _isNative = true;
     _fixedBackendName = name;
   }
 
   FunctionElement asFunctionElement() => null;
 
@@ skipping 2173 matching lines @@
   }
 
   void forEachBackendMember(void f(Element member)) {
     backendMembers.forEach(f);
   }
 
   bool implementsFunction(Compiler compiler) {
     return asInstanceOf(compiler.functionClass) != null || callType != null;
   }
 
-  bool get isNative => nativeTagInfo != null;
+  bool get isNative => nativeTagInfo != null || isJsInterop;
 
   void setNative(String name) {
     // TODO(johnniwinther): Assert that this is only called once. The memory
     // compiler copies pre-processed elements into a new compiler through
     // [Compiler.onLibraryScanned] and thereby causes multiple calls to this
     // method.
     assert(invariant(this, nativeTagInfo == null || nativeTagInfo == name,
         message: "Native tag info set inconsistently on $this: "
                  "Existing name '$nativeTagInfo', new name '$name'."));
     nativeTagInfo = name;
@@ skipping 481 matching lines @@
   AstElement get definingElement;
 
   bool get hasResolvedAst => definingElement.hasTreeElements;
 
   ResolvedAst get resolvedAst {
     return new ResolvedAst(declaration,
         definingElement.node, definingElement.treeElements);
   }
 
 }