Add MakeUnique from chromium and change StunMessage::AddAttribute to take a unique_ptr.

webrtc/p2p/base/stunrequest.cc

Index: webrtc/p2p/base/stunrequest.cc
diff --git a/webrtc/p2p/base/stunrequest.cc b/webrtc/p2p/base/stunrequest.cc
index ef2bee8aa819c251f7920df001666867912dc9dc..d3336fa8d7b8c84e87068f5ce7b5a4b8252da08d 100644
--- a/webrtc/p2p/base/stunrequest.cc
+++ b/webrtc/p2p/base/stunrequest.cc
@@ -16,6 +16,7 @@
 #include "webrtc/base/checks.h"
 #include "webrtc/base/helpers.h"
 #include "webrtc/base/logging.h"
+#include "webrtc/base/ptr_util.h"
 #include "webrtc/base/stringencode.h"
 
 namespace cricket {
@@ -189,8 +190,8 @@ StunRequest::~StunRequest() {
 void StunRequest::Construct() {
   if (msg_->type() == 0) {
     if (!origin_.empty()) {
-      msg_->AddAttribute(new StunByteStringAttribute(STUN_ATTR_ORIGIN,
-          origin_));
+      msg_->AddAttribute(
+          rtc::MakeUnique<StunByteStringAttribute>(STUN_ATTR_ORIGIN, origin_));
     }
     Prepare(msg_);
     RTC_DCHECK(msg_->type() != 0);