Make Network Predictor skip empty urls

net/http/http_stream_factory_impl.cc

Index: net/http/http_stream_factory_impl.cc
diff --git a/net/http/http_stream_factory_impl.cc b/net/http/http_stream_factory_impl.cc
index 25799331eb688be94fe6e8656442ae253e10ce86..669f04fdbbe93aea47312a1abb141a1a3d4c2cb1 100644
--- a/net/http/http_stream_factory_impl.cc
+++ b/net/http/http_stream_factory_impl.cc
@@ -194,6 +194,8 @@ HttpStreamRequest* HttpStreamFactoryImpl::RequestStreamInternal(
 void HttpStreamFactoryImpl::PreconnectStreams(
     int num_streams,
     const HttpRequestInfo& request_info) {
+  DCHECK(request_info.url.is_valid());
+
   AddJobControllerCountToHistograms();
 
   SSLConfig server_ssl_config;