Fix bugs in HttpBody detected by the analyzer

sdk/lib/io/http_body.dart

Index: sdk/lib/io/http_body.dart
diff --git a/sdk/lib/io/http_body.dart b/sdk/lib/io/http_body.dart
index 809075e202b46aca1e35883453e96e87706f870a..7a8a4942f1b6d13204c83a71c3065e6e9649669a 100644
--- a/sdk/lib/io/http_body.dart
+++ b/sdk/lib/io/http_body.dart
@@ -39,7 +39,9 @@ part of dart.io;
  */
 class HttpBodyHandler
     implements StreamTransformer<HttpRequest, HttpRequestBody> {
-  factory HttpBodyHandler() => new _HttpBodyHandler();
+  var _transformer;
+
+  HttpBodyHandler() : _transformer = new _HttpBodyHandlerTransformer();
 
   /**
    * Process and parse an incoming [HttpRequest]. The returned [HttpRequestBody]
@@ -56,6 +58,10 @@ class HttpBodyHandler
       HttpClientResponse response) {
     return _HttpBodyHandler.processResponse(response);
   }
+
+  Stream<HttpRequestBody> bind(Stream<HttpRequest> stream) {
+    return _transformer.bind(stream);
+  }
 }