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

pkg/compiler/lib/src/native/native.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 native;
 
 import '../compiler.dart' show Compiler;
 import '../elements/elements.dart';
 
 export 'behavior.dart';
 export 'enqueue.dart';
 export 'js.dart';
 export 'scanner.dart';
 export 'ssa.dart';
 
 const Iterable<String> _allowedDartSchemePaths = const <String>[
   'async',
   'html',
   'html_common',
   'indexed_db',
   'js',
+  'js_util',
   'svg',
   '_native_typed_data',
   'web_audio',
   'web_gl',
   'web_sql'
 ];
 
 bool maybeEnableNative(Compiler compiler, LibraryElement library) {
   bool allowedTestLibrary() {
     String scriptName = library.entryCompilationUnit.script.name;
     return scriptName.contains('sdk/tests/compiler/dart2js_native') ||
         scriptName.contains('sdk/tests/compiler/dart2js_extra');
   }
   bool allowedDartLibary() {
     Uri uri = library.canonicalUri;
     if (uri.scheme != 'dart') return false;
     return _allowedDartSchemePaths.contains(uri.path);
   }
 
   return allowedTestLibrary() ||
       allowedDartLibary() ||
       compiler.options.allowNativeExtensions;
 }