Make JSON parsing work as a chunked conversion sink.

sdk/lib/_internal/compiler/js_lib/convert_patch.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.
 
 // Patch file for dart:convert library.
 
 import 'dart:_js_helper' show patch;
 import 'dart:_foreign_helper' show JS;
 import 'dart:_interceptors' show JSExtendableArray;
 import 'dart:_internal' show MappedIterable;
@@ skipping 319 matching lines @@
       => JS('', '#[#]', object, key);
   static _setProperty(object, String key, value)
       => JS('', '#[#]=#', object, key, value);
   static List _getPropertyNames(object)
       => JS('JSExtendableArray', 'Object.keys(#)', object);
   static bool _isUnprocessed(object)
       => JS('bool', 'typeof(#)=="undefined"', object);
   static _newJavaScriptObject()
       => JS('=Object', 'Object.create(null)');
 }
+
+@patch class JsonDecoder {
+  @patch
+  StringConversionSink startChunkedConversion(Sink<Object> sink) {
+    return new _JsonDecoderSink(_reviver, sink);
+  }
+}
+
+/**
+ * Implements the chunked conversion from a JSON string to its corresponding
+ * object.
+ *
+ * The sink only creates one object, but its input can be chunked.
+ */
+// TODO(floitsch): don't accumulate everything before starting to decode.
+class _JsonDecoderSink extends _StringSinkConversionSink {
+  final _Reviver _reviver;
+  final Sink<Object> _sink;
+
+  _JsonDecoderSink(this._reviver, this._sink)
+      : super(new StringBuffer());
+
+  void close() {
+    super.close();
+    StringBuffer buffer = _stringSink;
+    String accumulated = buffer.toString();
+    buffer.clear();
+    Object decoded = _parseJson(accumulated, _reviver);
+    _sink.add(decoded);
+    _sink.close();
+  }
+}