Replace scoped_ptr with unique_ptr everywhere

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/1937693002
Cr-Commit-Position: refs/heads/master@{#12581}
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCMediaConstraints.mm b/webrtc/sdk/objc/Framework/Classes/RTCMediaConstraints.mm
index 7a7cdf1..11be2ec 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCMediaConstraints.mm
+++ b/webrtc/sdk/objc/Framework/Classes/RTCMediaConstraints.mm
@@ -12,6 +12,8 @@
 
 #import "NSString+StdString.h"
 
+#include <memory>
+
 namespace webrtc {
 
 MediaConstraints::~MediaConstraints() {}
@@ -62,7 +64,7 @@
 
 #pragma mark - Private
 
-- (rtc::scoped_ptr<webrtc::MediaConstraints>)nativeConstraints {
+- (std::unique_ptr<webrtc::MediaConstraints>)nativeConstraints {
   webrtc::MediaConstraintsInterface::Constraints mandatory =
       [[self class] nativeConstraintsForConstraints:_mandatory];
   webrtc::MediaConstraintsInterface::Constraints optional =
@@ -70,7 +72,7 @@
 
   webrtc::MediaConstraints *nativeConstraints =
       new webrtc::MediaConstraints(mandatory, optional);
-  return rtc::scoped_ptr<webrtc::MediaConstraints>(nativeConstraints);
+  return std::unique_ptr<webrtc::MediaConstraints>(nativeConstraints);
 }
 
 + (webrtc::MediaConstraintsInterface::Constraints)