Change the interface of GetAlternativeServicesFor, always return the best Alt-Svc entry.

net/quic/quic_stream_factory.cc

Index: net/quic/quic_stream_factory.cc
diff --git a/net/quic/quic_stream_factory.cc b/net/quic/quic_stream_factory.cc
index 2443381e3e4f20654a2aba7b839876f455279a42..10600cc503c873105599e114cf38bdcbe54685ee 100644
--- a/net/quic/quic_stream_factory.cc
+++ b/net/quic/quic_stream_factory.cc
@@ -25,7 +25,6 @@
 #include "net/cert/ct_verifier.h"
 #include "net/dns/host_resolver.h"
 #include "net/dns/single_request_host_resolver.h"
-#include "net/http/http_server_properties.h"
 #include "net/quic/crypto/channel_id_chromium.h"
 #include "net/quic/crypto/proof_verifier_chromium.h"
 #include "net/quic/crypto/properties_based_quic_server_info.h"
@@ -707,6 +706,19 @@ void QuicStreamFactory::set_quic_server_info_factory(
   quic_server_info_factory_.reset(quic_server_info_factory);
 }
 
+bool QuicStreamFactory::CanUseExistingSession(QuicServerId server_id,
+                                              PrivacyMode privacy_mode,
+                                              StringPiece origin_host) {
+  // TODO(zhongyi): crbug.com/498823 - delete active_sessions_.empty() checks.
+  if (active_sessions_.empty())
+    return false;
+  SessionMap::iterator it = active_sessions_.find(server_id);
+  if (it == active_sessions_.end())
+    return false;
+  QuicChromiumClientSession* session = it->second;
+  return session->CanPool(origin_host.as_string(), privacy_mode);
+}
+
 int QuicStreamFactory::Create(const HostPortPair& host_port_pair,
                               PrivacyMode privacy_mode,
                               int cert_verify_flags,