Add browser-compatible version.

lib/src/resource_loader.dart

+// 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.
+
+import "dart:async" show Future, Stream;
+import "dart:convert" show Encoding;
+
+/// Resource loading strategy.
+///
+/// An abstraction of the functionality needed to load resources.
+///
+/// Implementations of this interface decide which URI schemes they support.
+abstract class ResourceLoader {
+  /// Reads the file located by [uri] as a stream of bytes.
+  Stream<List<int>> openRead(Uri uri);
+
+  /// Reads the file located by [uri] as a list of bytes.
+  Future<List<int>> readAsBytes(Uri uri);
+
+  /// Reads the file located by [uri] as a [String].
+  ///
+  /// The file bytes are decoded using [encoding], if provided.
+  ///
+  /// If [encoding] is omitted, the default for the `file:` scheme is UTF-8.
+  /// For `http`, `https` and `data` URIs, the Content-Type header's charset
+  /// is used, if available and recognized by [Encoding.getByName],
+  /// otherwise it defaults to Latin-1 for `http` and `https`
+  /// and to ASCII for `data` URIs.
+  Future<String> readAsString(Uri uri, {Encoding encoding});
+}
+