Fix QuicHttpStream reporting negative sent bytes.

net/quic/chromium/quic_http_stream.cc

Index: net/quic/chromium/quic_http_stream.cc
diff --git a/net/quic/chromium/quic_http_stream.cc b/net/quic/chromium/quic_http_stream.cc
index 140dbc0af1f2284cfa956dcb514caa5cc1dc5237..8e27f4386b278c6eda60be6263b31ddf99515c2d 100644
--- a/net/quic/chromium/quic_http_stream.cc
+++ b/net/quic/chromium/quic_http_stream.cc
@@ -608,12 +608,13 @@ int QuicHttpStream::DoSendHeaders() {
   bool has_upload_data = request_body_stream_ != nullptr;
 
   next_state_ = STATE_SEND_HEADERS_COMPLETE;
-  size_t frame_len = stream_->WriteHeaders(std::move(request_headers_),
-                                           !has_upload_data, nullptr);
-  headers_bytes_sent_ += frame_len;
+  int rv = stream_->WriteHeaders(std::move(request_headers_), !has_upload_data,
+                                 nullptr);
+  if (rv > 0)
+    headers_bytes_sent_ += rv;
 
   request_headers_ = SpdyHeaderBlock();
-  return static_cast<int>(frame_len);
+  return rv;
 }
 
 int QuicHttpStream::DoSendHeadersComplete(int rv) {