Redo StreamTransformers so they work with Stack traces.

pkg/http_server/lib/src/http_body_impl.dart

Index: pkg/http_server/lib/src/http_body_impl.dart
diff --git a/pkg/http_server/lib/src/http_body_impl.dart b/pkg/http_server/lib/src/http_body_impl.dart
index f3ffa9e7252d7d7a2c1d8c826e5ab7e2cdcb0566..3c4a5fae66b79622be6cee22eacdf4b5bb230d7d 100644
--- a/pkg/http_server/lib/src/http_body_impl.dart
+++ b/pkg/http_server/lib/src/http_body_impl.dart
@@ -5,14 +5,33 @@
 part of http_server;
 
 class _HttpBodyHandlerTransformer
-    extends StreamEventTransformer<HttpRequest, HttpRequestBody> {
+    implements StreamTransformer<HttpRequest, HttpRequestBody> {
   final Encoding _defaultEncoding;
-  _HttpBodyHandlerTransformer(this._defaultEncoding);
 
-  void handleData(HttpRequest request, EventSink<HttpRequestBody> sink) {
+  const _HttpBodyHandlerTransformer(this._defaultEncoding);
+
+  Stream<HttpRequestBody> bind(Stream<HttpRequest> stream) {
+    return new Stream<HttpRequestBody>.eventTransformed(
+        stream,
+        (EventSink<HttpRequestBody> sink) =>
+            new _HttpBodyHandlerTransformerSink(_defaultEncoding, sink));
+  }
+}
+
+class _HttpBodyHandlerTransformerSink implements EventSink<HttpRequest> {
+  final Encoding _defaultEncoding;
+  final EventSink<HttpRequestBody> _outSink;
+
+  _HttpBodyHandlerTransformerSink(this._defaultEncoding, this._outSink);
+
+  void add(HttpRequest request) {
     _HttpBodyHandler.processRequest(request, _defaultEncoding)
-        .then(sink.add, onError: sink.addError);
+        .then(_outSink.add, onError: _outSink.addError);
+  }
+  void addError(Object error, [StackTrace stackTrace]) {
+    _outSink.addError(error, stackTrace);
   }
+  void close() => _outSink.close();
 }
 
 class _HttpBodyHandler {