remoting: Add out-of-line copy ctors for complex classes.

remoting/signaling/xmpp_signal_strategy.cc

Index: remoting/signaling/xmpp_signal_strategy.cc
diff --git a/remoting/signaling/xmpp_signal_strategy.cc b/remoting/signaling/xmpp_signal_strategy.cc
index fbc5373dfc9ef2ce93b2f5288c20b702bd75a1fb..10aea02a1ddad8ae266348d82b6aaf594c4681d9 100644
--- a/remoting/signaling/xmpp_signal_strategy.cc
+++ b/remoting/signaling/xmpp_signal_strategy.cc
@@ -46,6 +46,9 @@ XmppSignalStrategy::XmppServerConfig::XmppServerConfig()
     : port(kDefaultXmppPort), use_tls(true) {
 }
 
+XmppSignalStrategy::XmppServerConfig::XmppServerConfig(
+    const XmppServerConfig& other) = default;
+
 XmppSignalStrategy::XmppServerConfig::~XmppServerConfig() {
 }