Add transformer support to Converters.

tests/lib/convert/streamed_conversion_json_encode1_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 '../../async_helper.dart';
 
 final TESTS = [
     [ 5, '5' ],
     [ -42, '-42' ],
     [ 3.14, '3.14' ],
     [ true, 'true' ],
     [ false, 'false' ],
     [ null, 'null' ],
     [ 'quote"or\'', '"quote\\"or\'"' ],
     [ '', '""' ],
     [ [], "[]" ],
     [ [3, -4.5, true, "hi", false], '[3,-4.5,true,"hi",false]' ],
     [ [null], "[null]" ],
     [ [[null]], "[[null]]" ],
     [ [[3]], "[[3]]" ],
     [ {}, "{}" ],
     [ { "x": 3, "y": 4.5, "z": "hi", "u": true, "v": false },
       '{"x":3,"y":4.5,"z":"hi","u":true,"v":false}' ],
     [ { "x": null }, '{"x":null}' ],
     [ { "x": {} }, '{"x":{}}' ],
     // Note that -0.0 won't be treated the same in JS. The Json spec seems to
     // allow it, though.
     [ { "hi there": 499, "'":-0.0 }, '{"hi there":499,"\'":-0.0}' ],
     [ r'\foo', r'"\\foo"' ],
   ];
 
-class MyStringConversionSink extends StringConversionSinkBase {
-  var buffer = new StringBuffer();
-  var callback;
-
-  MyStringConversionSink(this.callback);
-
-  addSlice(str, start, end, bool isLast) {
-    buffer.write(str.substring(start, end));
-    if (isLast) close();
-  }
-
-  close() {
-    callback(buffer.toString());
-  }
+Stream<String> encode(Object o) {
+  var encoder = new JsonEncoder();
+  StreamController controller;
+  controller = new StreamController(onListen: () {
+    controller.add(o);
+    controller.close();
+  });
+  return controller.stream.transform(encoder);
 }
 
-String encode(Object o) {
-  var result;
-  var encoder = new JsonEncoder();
-  ChunkedConversionSink stringSink =
-      new MyStringConversionSink((x) => result = x);
-  var objectSink = new JsonEncoder().startChunkedConversion(stringSink);
-  objectSink.add(o);
-  objectSink.close();
-  return result;
+void testNoPause(String expected, Object o) {
+  asyncStart();
+  Stream stream = encode(o);
+  stream.toList().then((list) {
+    StringBuffer buffer = new StringBuffer();
+    buffer.writeAll(list);
+    Expect.stringEquals(expected, buffer.toString());
+    asyncEnd();
+  });
 }
 
-String encode2(Object o) {
-  var result;
-  var encoder = new JsonEncoder();
-  ChunkedConversionSink stringSink =
-      new StringConversionSink.withCallback((x) => result = x);
-  var objectSink = encoder.startChunkedConversion(stringSink);
-  objectSink.add(o);
-  objectSink.close();
-  return result;
+void testWithPause(String expected, Object o) {
+  asyncStart();
+  Stream stream = encode(o);
+  StringBuffer buffer = new StringBuffer();
+  var sub;
+  sub = stream.listen((x) {
+    buffer.write(x);
+    sub.pause(new Future.delayed(Duration.ZERO));
+  }, onDone: () {
+    Expect.stringEquals(expected, buffer.toString());
+    asyncEnd();
+  });
 }
 
-main() {
+void main() {
   for (var test in TESTS) {
     var o = test[0];
     var expected = test[1];
-    Expect.equals(expected, encode(o));
-    Expect.equals(expected, encode2(o));
+    testNoPause(expected, o);
+    testWithPause(expected, o);
   }
 }