Add transformer support to Converters.

tests/lib/convert/streamed_conversion_json_utf8_decode_test.dart

+// Copyright (c) 2013, 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 "package:expect/expect.dart";
+import 'dart:async';
+import 'dart:convert';
+import 'json_unicode_tests.dart';
+import '../../async_helper.dart';
+
+final JSON_UTF8 = JSON.fuse(UTF8);
+
+bool isJsonEqual(o1, o2) {
+  if (o1 == o2) return true;
+  if (o1 is List && o2 is List) {
+    if (o1.length != o2.length) return false;
+    for (int i = 0; i < o1.length; i++) {
+      if (!isJsonEqual(o1[i], o2[i])) return false;
+    }
+    return true;
+  }
+  if (o1 is Map && o2 is Map) {
+    if (o1.length != o2.length) return false;
+    for (var key in o1.keys) {
+      Expect.isTrue(key is String);
+      if (!o2.containsKey(key)) return false;
+      if (!isJsonEqual(o1[key], o2[key])) return false;
+    }
+    return true;
+  }
+  return false;
+}
+
+Stream<Object> createStream(List<List<int>> chunks) {
+  var controller;
+  controller = new StreamController(onListen: () {
+    chunks.forEach(controller.add);
+    controller.close();
+  });
+  return controller.stream.transform(JSON_UTF8.decoder);
+}
+
+Stream<Object> decode(List<int> bytes) {
+  return createStream([bytes]);
+}
+
+Stream<Object> decodeChunked(List<int> bytes, int chunkSize) {
+  List<List<int>> chunked = <List<int>>[];
+  int i = 0;
+  while (i < bytes.length) {
+    if (i + chunkSize <= bytes.length) {
+      chunked.add(bytes.sublist(i, i + chunkSize));
+    } else {
+      chunked.add(bytes.sublist(i));
+    }
+    i += chunkSize;
+  }
+  return createStream(chunked);
+}
+
+void checkIsJsonEqual(expected, stream) {
+  asyncStart();
+  stream.single.then((o) {
+    Expect.isTrue(isJsonEqual(expected, o));
+    asyncEnd();
+  });
+}
+
+main() {
+  for (var test in JSON_UNICODE_TESTS) {
+    var bytes = test[0];
+    var o = test[1];
+    checkIsJsonEqual(o, decode(bytes));
+    checkIsJsonEqual(o, decodeChunked(bytes, 1));
+    checkIsJsonEqual(o, decodeChunked(bytes, 2));
+    checkIsJsonEqual(o, decodeChunked(bytes, 3));
+    checkIsJsonEqual(o, decodeChunked(bytes, 4));
+    checkIsJsonEqual(o, decodeChunked(bytes, 5));
+  }
+}