Replace scoped_ptr with unique_ptr in talk/

talk/app/webrtc/objc/RTCMediaStreamTrack.mm

Index: talk/app/webrtc/objc/RTCMediaStreamTrack.mm
diff --git a/talk/app/webrtc/objc/RTCMediaStreamTrack.mm b/talk/app/webrtc/objc/RTCMediaStreamTrack.mm
index c529f5a4b299016268bb4738bfaf1141ed333399..e0d5cae9daae655d1b98506993d5608c35cdb96b 100644
--- a/talk/app/webrtc/objc/RTCMediaStreamTrack.mm
+++ b/talk/app/webrtc/objc/RTCMediaStreamTrack.mm
@@ -32,6 +32,8 @@
 #import "RTCEnumConverter.h"
 #import "RTCMediaStreamTrack+Internal.h"
 
+#include <memory>
+
 namespace webrtc {
 
 class RTCMediaStreamTrackObserver : public ObserverInterface {
@@ -49,7 +51,7 @@ class RTCMediaStreamTrackObserver : public ObserverInterface {
 
 @implementation RTCMediaStreamTrack {
   rtc::scoped_refptr<webrtc::MediaStreamTrackInterface> _mediaTrack;
-  rtc::scoped_ptr<webrtc::RTCMediaStreamTrackObserver> _observer;
+  std::unique_ptr<webrtc::RTCMediaStreamTrackObserver> _observer;
 }
 
 @synthesize label;