[Not for review] Add TRACE_EVENTs and chrome://flags for preconnect

net/quic/chromium/quic_stream_factory.cc

Index: net/quic/chromium/quic_stream_factory.cc
diff --git a/net/quic/chromium/quic_stream_factory.cc b/net/quic/chromium/quic_stream_factory.cc
index 378985bbf25ad21af847fc2eace88b3fd1bbbe00..c4312ce705eb56378c119acc4f3a3d2252d804e9 100644
--- a/net/quic/chromium/quic_stream_factory.cc
+++ b/net/quic/chromium/quic_stream_factory.cc
@@ -537,6 +537,8 @@ int QuicStreamFactory::Job::DoConnect() {
 }
 
 int QuicStreamFactory::Job::DoConnectComplete(int rv) {
+  TRACE_EVENT1(kNetTracingCategory, "QuicStreamFactory::Job::DoConnectComplete",
+               "host", key_.destination().host());
   net_log_.EndEvent(NetLogEventType::QUIC_STREAM_FACTORY_JOB_CONNECT);
   if (session_ && session_->error() == QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT) {
     num_sent_client_hellos_ += session_->GetNumSentClientHellos();
@@ -587,6 +589,8 @@ int QuicStreamRequest::Request(const HostPortPair& destination,
                                QuicStringPiece method,
                                const NetLogWithSource& net_log,
                                const CompletionCallback& callback) {
+  TRACE_EVENT1(kNetTracingCategory, "QuicStreamRequest::Request", "host",
+               destination.host());
   DCHECK(callback_.is_null());
   DCHECK(factory_);
   server_id_ = QuicServerId(HostPortPair::FromURL(url), privacy_mode);