Replace scoped_ptr with unique_ptr in webrtc/common_video/

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1749103003

Cr-Commit-Position: refs/heads/master@{#11838}
diff --git a/webrtc/video_decoder.h b/webrtc/video_decoder.h
index e99183f..4f25e1f 100644
--- a/webrtc/video_decoder.h
+++ b/webrtc/video_decoder.h
@@ -11,6 +11,7 @@
 #ifndef WEBRTC_VIDEO_DECODER_H_
 #define WEBRTC_VIDEO_DECODER_H_
 
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -116,7 +117,7 @@
   VideoCodec codec_settings_;
   int32_t number_of_cores_;
   std::string fallback_implementation_name_;
-  rtc::scoped_ptr<VideoDecoder> fallback_decoder_;
+  std::unique_ptr<VideoDecoder> fallback_decoder_;
   DecodedImageCallback* callback_;
 };