Fix a bug in [http.BaseRequest.send]'s content length handling.

pkg/http/lib/src/base_request.dart

Index: pkg/http/lib/src/base_request.dart
diff --git a/pkg/http/lib/src/base_request.dart b/pkg/http/lib/src/base_request.dart
index a52b9c27b6aafe106a12b591b44ecf7d35ff5a35..ba87e52b3ec12de4dca723698eca0e5982de1766 100644
--- a/pkg/http/lib/src/base_request.dart
+++ b/pkg/http/lib/src/base_request.dart
@@ -115,12 +115,10 @@ abstract class BaseRequest {
     var client = new Client();
     return client.send(this).then((response) {
       var stream = onDone(response.stream, client.close);
-      var contentLength = response.contentLength < 0 ?
-          null : response.contentLength;
       return new StreamedResponse(
           new ByteStream(stream),
           response.statusCode,
-          contentLength: contentLength,
+          contentLength: response.contentLength,
           request: response.request,
           headers: response.headers,
           isRedirect: response.isRedirect,