Mark resource as experimental

sdk/lib/core/resource.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.
 
 part of dart.core;
 
 /**
  * A resource that can be read into the program.
  *
+ * WARNING: This API is _experimental_,
+ * and it may be changed or removed in future releases
+ *
  * A resource is data that can be located using a URI and read into
  * the program at runtime.
  * The URI may use the `package` scheme to read resources provided
  * along with package sources.
  */
 abstract class Resource {
   /**
    * Creates a resource object with the given [uri] as location.
    *
    * The `uri` is a string containing a valid URI.
@@ skipping 23 matching lines @@
   Future<List<int>> readAsBytes();
 
   /**
    * Read the resource content as a string.
    *
    * The content is decoded into a string using an [Encoding].
    * If no other encoding is provided, it defaults to UTF-8.
    */
   Future<String> readAsString({Encoding encoding});
 }