Migrate modules/video_coding to webrtc::Mutex.

Bug: webrtc:11567
Change-Id: I8023fbe7595f7ba8ae7c7db3583fc2e560ec3df2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/178803
Commit-Queue: Markus Handell <handellm@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31644}
diff --git a/modules/video_coding/fec_controller_default.h b/modules/video_coding/fec_controller_default.h
index 02c0ec0..6b9e8eb 100644
--- a/modules/video_coding/fec_controller_default.h
+++ b/modules/video_coding/fec_controller_default.h
@@ -20,7 +20,7 @@
 #include "api/fec_controller.h"
 #include "modules/video_coding/media_opt_util.h"
 #include "rtc_base/constructor_magic.h"
-#include "rtc_base/critical_section.h"
+#include "rtc_base/synchronization/mutex.h"
 #include "rtc_base/thread_annotations.h"
 #include "system_wrappers/include/clock.h"
 
@@ -54,10 +54,10 @@
   enum { kBitrateAverageWinMs = 1000 };
   Clock* const clock_;
   VCMProtectionCallback* protection_callback_;
-  rtc::CriticalSection crit_sect_;
+  Mutex mutex_;
   std::unique_ptr<media_optimization::VCMLossProtectionLogic> loss_prot_logic_
-      RTC_GUARDED_BY(crit_sect_);
-  size_t max_payload_size_ RTC_GUARDED_BY(crit_sect_);
+      RTC_GUARDED_BY(mutex_);
+  size_t max_payload_size_ RTC_GUARDED_BY(mutex_);
   RTC_DISALLOW_COPY_AND_ASSIGN(FecControllerDefault);
   const float overhead_threshold_;
 };