Add chunked conversion to converters.

sdk/lib/convert/chunked_conversion.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.
+
+part of dart.convert;
+
+typedef void _ChunkedConversionCallback<T>(T accumulated);
+
+/**
+ * A [ChunkedConversionSink] is used to transmit data more efficiently between
+ * two converters during chunked conversions.
+ */
+abstract class ChunkedConversionSink<T> {
+  ChunkedConversionSink();
+  factory ChunkedConversionSink.withCallback(
+      void callback(List<T> accumulated)) = _SimpleCallbackSink;
+
+  /**
+   * Adds chunked data to this sink.
+   *
+   * This method is also used when converters are used as [StreamTransformer]s.
+   */
+  void add(T chunk);
+
+  /**
+   * Closes the sink.
+   *
+   * This signals the end of the chunked conversion. This method is called
+   * when converters are used as [StreamTransformer]'s.
+   */
+  void close();
+}
+
+/**
+ * This class accumulates all chunks and invokes a callback with a list of
+ * the chunks when the sink is closed.
+ *
+ * This class can be used to terminate a chunked conversion.
+ */
+class _SimpleCallbackSink<T> extends ChunkedConversionSink<T> {
+  final _ChunkedConversionCallback<List<T>> _callback;
+  final List<T> _accumulated = <T>[];
+
+  _SimpleCallbackSink(this._callback);
+
+  void add(T chunk) { _accumulated.add(chunk); }
+  void close() { _callback(_accumulated); }
+}