Add browser-compatible version.

lib/src/io.dart

-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
-// dart:io based strategy for loading resources.
-
 import "dart:async" show Future, Stream;
 import "dart:convert" show Encoding, LATIN1, UTF8;
 import "dart:io" show
     File, HttpClient, HttpClientResponse, HttpClientRequest, HttpHeaders;
 import "dart:typed_data" show Uint8List;
+
 import "package:typed_data/typed_buffers.dart" show Uint8Buffer;
 
 /// Read the bytes of a URI as a stream of bytes.
 Stream<List<int>> readAsStream(Uri uri) async* {
   if (uri.scheme == "file") {
     yield* new File.fromUri(uri).openRead();
     return;
   }
   if (uri.scheme == "http" || uri.scheme == "https") {
     HttpClientResponse response = await _httpGet(uri);
@@ skipping 61 matching lines @@
     return uri.data.contentAsString(encoding: encoding);
   }
   throw new UnsupportedError("Unsupported scheme: $uri");
 }
 
 Future<HttpClientResponse> _httpGet(Uri uri) async {
   HttpClientRequest request = await new HttpClient().getUrl(uri);
     request.headers.set(HttpHeaders.ACCEPT, "application/octet-stream, */*");
   return request.close();
 }