Convert //media/audio from scoped_ptr to std::unique_ptr

media/audio/mock_audio_manager.cc

Index: media/audio/mock_audio_manager.cc
diff --git a/media/audio/mock_audio_manager.cc b/media/audio/mock_audio_manager.cc
index cca34d08cd5cd9817dd99063829cc4948382375a..4528bafc9ea3f9e5973c087f0cc20d5f0e51265c 100644
--- a/media/audio/mock_audio_manager.cc
+++ b/media/audio/mock_audio_manager.cc
@@ -90,9 +90,9 @@ std::string MockAudioManager::GetAssociatedOutputDeviceID(
   return std::string();
 }
 
-scoped_ptr<AudioLog> MockAudioManager::CreateAudioLog(
+std::unique_ptr<AudioLog> MockAudioManager::CreateAudioLog(
     AudioLogFactory::AudioComponent component) {
-  return scoped_ptr<AudioLog>();
+  return nullptr;
 }
 
 }  // namespace media.