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/RTCVideoRendererAdapter.mm b/webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm
index 1d64cd8..4976ba9 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm
+++ b/webrtc/sdk/objc/Framework/Classes/RTCVideoRendererAdapter.mm
@@ -12,6 +12,8 @@
 
 #import "RTCVideoFrame+Private.h"
 
+#include <memory>
+
 #include "webrtc/media/engine/webrtcvideoframe.h"
 
 namespace webrtc {
@@ -60,7 +62,7 @@
 }
 
 @implementation RTCVideoRendererAdapter {
-  rtc::scoped_ptr<webrtc::VideoRendererAdapter> _adapter;
+  std::unique_ptr<webrtc::VideoRendererAdapter> _adapter;
 }
 
 @synthesize videoRenderer = _videoRenderer;