Add JSNative utility class with static methods methods to efficiently manipulate typed JSInterop ob…

pkg/js/lib/js.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.
 
 /// Allows interoperability with Javascript APIs.
 library js;
 
-export 'dart:js' show allowInterop, allowInteropCaptureThis;
+export 'dart:js' show allowInterop, allowInteropCaptureThis, JSNative;
 
 /// A metadata annotation that indicates that a Library, Class, or member is
 /// implemented directly in JavaScript. All external members of a class or
 /// library with this annotation implicitly have it as well.
 ///
 /// Specifying [name] customizes the JavaScript name to use. By default the
 /// dart name is used. It is not valid to specify a custom [name] for class
 /// instance members.
 class JS {
   final String name;
   const JS([this.name]);
 }
 
 class _Anonymous {
   const _Anonymous();
 }
 
 /// A metadata annotation that indicates that a @JS annotated class is
 /// structural and does not have a known JavaScript prototype.
 ///
 /// Factory constructors for anonymous JavaScript classes desugar to creating
 /// JavaScript object literals with name-value pairs corresponding to the
 /// parameter names and values.
 const _Anonymous anonymous = const _Anonymous();