Replace the remaining scoped_ptr with unique_ptr in webrtc/modules/

(This is a re-land of https://codereview.webrtc.org/1921233002, which
got reverted for breaking Chromium.)

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1923133002

Cr-Commit-Position: refs/heads/master@{#12522}

webrtc/modules/audio_coding/neteq/decoder_database.h

@@ -12,6 +12,7 @@
 #define WEBRTC_MODULES_AUDIO_CODING_NETEQ_DECODER_DATABASE_H_
 
 #include <map>
+#include <memory>
 #include <string>
 
 #include "webrtc/base/constructormagic.h"