Merge all http-outgoing transfomers into _HttpOutgoing, including simpler(better) buffering.

sdk/lib/io/io_sink.dart

Index: sdk/lib/io/io_sink.dart
diff --git a/sdk/lib/io/io_sink.dart b/sdk/lib/io/io_sink.dart
index e2ea2bd63abb9bc065d8108862febc832f6c074a..74d12b475c032497e22378729bb08c3def0919a5 100644
--- a/sdk/lib/io/io_sink.dart
+++ b/sdk/lib/io/io_sink.dart
@@ -110,10 +110,18 @@ class _StreamSinkImpl<T> implements StreamSink<T> {
   }
 
   Future flush() {
+    if (_isBound) {
+      throw new StateError("StreamSink is bound to a stream");
+    }
+    if (_controllerInstance == null) return new Future.value(this);
     // Adding an empty stream-controller will return a future that will complete
     // when all data is done.
-    var controller = new StreamController()..close();
-    return addStream(controller.stream).then((_) => this);
+    _isBound = true;
+    var future = _controllerCompleter.future;
+    _controllerInstance.close();
+    return future.whenComplete(() {
+          _isBound = false;
+        });
   }
 
   Future close() {
@@ -165,7 +173,7 @@ class _StreamSinkImpl<T> implements StreamSink<T> {
               (_) {
                 if (_isBound) {
                   // A new stream takes over - forward values to that stream.
-                  _controllerCompleter.complete();
+                  _controllerCompleter.complete(this);
                   _controllerCompleter = null;
                   _controllerInstance = null;
                 } else {
@@ -221,7 +229,7 @@ class _IOSinkImpl extends _StreamSinkImpl<List<int>> implements IOSink {
       }
     }
     if (string.isEmpty) return;
-    add(_encoding.encode(string));
+    add(encoding.encode(string));
   }
 
   void writeAll(Iterable objects, [String separator = ""]) {