Replace the remaining scoped_ptr with unique_ptr in webrtc/modules/

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1921233002

Cr-Commit-Position: refs/heads/master@{#12511}
diff --git a/webrtc/modules/utility/source/process_thread_impl.h b/webrtc/modules/utility/source/process_thread_impl.h
index 2855ed9..330aec9 100644
--- a/webrtc/modules/utility/source/process_thread_impl.h
+++ b/webrtc/modules/utility/source/process_thread_impl.h
@@ -33,7 +33,7 @@
   void Stop() override;
 
   void WakeUp(Module* module) override;
-  void PostTask(rtc::scoped_ptr<ProcessTask> task) override;
+  void PostTask(std::unique_ptr<ProcessTask> task) override;
 
   void RegisterModule(Module* module) override;
   void DeRegisterModule(Module* module) override;