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

sdk/lib/js_util/dartium/js_util_dartium.dart

Index: sdk/lib/js_util/dartium/js_util_dartium.dart
diff --git a/sdk/lib/js_util/dartium/js_util_dartium.dart b/sdk/lib/js_util/dartium/js_util_dartium.dart
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+// Copyright (c) 2016, 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.
+
+/// Utility methods to efficiently manipulate typed JSInterop objects in cases
+/// where the name to call is not known at runtime. You should only use these
+/// methods when the same effect cannot be achieved with @JS annotations.
+/// These methods would be extension methods on JSObject if Dart supported
+/// extension methods.
+library dart.js_util;
+
+import 'dart:js';
+
+/// WARNING: performance of this method is much worse than other uitil
+/// methods in this library. Only use this method as a last resort.
+///
+/// Recursively converts a JSON-like collection of Dart objects to a
+/// collection of JavaScript objects and returns a [JsObject] proxy to it.
+///
+/// [object] must be a [Map] or [Iterable], the contents of which are also
+/// converted. Maps and Iterables are copied to a new JavaScript object.
+/// Primitives and other transferrable values are directly converted to their
+/// JavaScript type, and all other objects are proxied.
+jsify(object) {
+  if ((object is! Map) && (object is! Iterable)) {
+    throw new ArgumentError("object must be a Map or Iterable");
+  }
+  return JsNative.jsify(object);
+}
+
+JSObject newObject() => JsNative.newObject();
+
+hasProperty(JSObject o, name) => JsNative.hasProperty(o, name);
+getProperty(JSObject o, name) => JsNative.getProperty(o, name);
+setProperty(JSObject o, name, value) => JsNative.setProperty(o, name, value);
+callMethod(JSObject o, String method, List args) => JsNative.callMethod(o, method, args);
+instanceof(JSObject o, Function type) => JsNative.instanceof(o, type);
+callConstructor(JSObject constructor, List args) => JsNative.callConstructor(constructor, args);