Make utf8 decoder non-buffered.

tests/lib/convert/chunked_conversion_utf89_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:convert';
+
+class MySink extends ChunkedConversionSink<String> {
+  final Function _add;
+  final Function _close;
+
+  MySink(this._add, this._close);
+
+  void add(x) { _add(x); }
+  void close() { _close(); }
+}
+
+main() {
+  // Make sure the UTF-8 decoder works eagerly.
+  String lastString;
+  bool isClosed = false;
+  ChunkedConversionSink sink = new MySink((x) => lastString = x,
+                                          () => isClosed = true);
+  var byteSink = new Utf8Decoder().startChunkedConversion(sink);
+  byteSink.add("abc".codeUnits);
+  Expect.equals("abc", lastString);
+  byteSink.add([0x61, 0xc3]);  // 'a' followed by first part of Î.
+  Expect.equals("a", lastString);
+  byteSink.add([0x8e]);  // second part of Î.
+  Expect.equals("Î", lastString);
+  Expect.isFalse(isClosed);
+  byteSink.close();
+  Expect.isTrue(isClosed);
+}