Replace scoped_ptr with unique_ptr in webrtc/p2p/

But keep #including scoped_ptr.h in .h files, so as not to break
WebRTC users who expect those .h files to give them rtc::scoped_ptr.

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1923163003

Cr-Commit-Position: refs/heads/master@{#12532}
diff --git a/webrtc/p2p/base/stunport.h b/webrtc/p2p/base/stunport.h
index a0eba51..cd844aa 100644
--- a/webrtc/p2p/base/stunport.h
+++ b/webrtc/p2p/base/stunport.h
@@ -11,6 +11,7 @@
 #ifndef WEBRTC_P2P_BASE_STUNPORT_H_
 #define WEBRTC_P2P_BASE_STUNPORT_H_
 
+#include <memory>
 #include <string>
 
 #include "webrtc/p2p/base/port.h"
@@ -224,7 +225,7 @@
   StunRequestManager requests_;
   rtc::AsyncPacketSocket* socket_;
   int error_;
-  rtc::scoped_ptr<AddressResolver> resolver_;
+  std::unique_ptr<AddressResolver> resolver_;
   bool ready_;
   int stun_keepalive_delay_;
   int stun_keepalive_lifetime_;