Revert of Replace scoped_ptr with unique_ptr in webrtc/common_audio/

webrtc/common_audio/audio_converter.cc

Index: webrtc/common_audio/audio_converter.cc
diff --git a/webrtc/common_audio/audio_converter.cc b/webrtc/common_audio/audio_converter.cc
index d6334b38664f4ceb502cead6d5ae90af7290629d..9ebfabc2860c6aeee019b9bc26615ae23d2d9070 100644
--- a/webrtc/common_audio/audio_converter.cc
+++ b/webrtc/common_audio/audio_converter.cc
@@ -136,11 +136,11 @@
   ScopedVector<ChannelBuffer<float>> buffers_;
 };
 
-std::unique_ptr<AudioConverter> AudioConverter::Create(size_t src_channels,
+rtc::scoped_ptr<AudioConverter> AudioConverter::Create(size_t src_channels,
                                                        size_t src_frames,
                                                        size_t dst_channels,
                                                        size_t dst_frames) {
-  std::unique_ptr<AudioConverter> sp;
+  rtc::scoped_ptr<AudioConverter> sp;
   if (src_channels > dst_channels) {
     if (src_frames != dst_frames) {
       ScopedVector<AudioConverter> converters;