remove more CriticalSectionWrappers.

BUG=webrtc:7035

Review-Url: https://codereview.webrtc.org/2779623002
Cr-Commit-Position: refs/heads/master@{#17392}
diff --git a/webrtc/modules/video_coding/media_optimization.h b/webrtc/modules/video_coding/media_optimization.h
index 290636f..bc48300 100644
--- a/webrtc/modules/video_coding/media_optimization.h
+++ b/webrtc/modules/video_coding/media_optimization.h
@@ -101,7 +101,7 @@
   uint32_t SentFrameRateInternal() EXCLUSIVE_LOCKS_REQUIRED(crit_sect_);
 
   // Protect all members.
-  std::unique_ptr<CriticalSectionWrapper> crit_sect_;
+  rtc::CriticalSection crit_sect_;
 
   Clock* clock_ GUARDED_BY(crit_sect_);
   int32_t max_bit_rate_ GUARDED_BY(crit_sect_);