Migrate rtc_base to webrtc::Mutex.

Bug: webrtc:11567
Change-Id: Ib8630e0cf1266e7c3f8ce718e1ed9f8848f42ec8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/178806
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31682}
diff --git a/rtc_base/event_tracer_unittest.cc b/rtc_base/event_tracer_unittest.cc
index 79cc9c0..f4d41e4 100644
--- a/rtc_base/event_tracer_unittest.cc
+++ b/rtc_base/event_tracer_unittest.cc
@@ -10,7 +10,7 @@
 
 #include "rtc_base/event_tracer.h"
 
-#include "rtc_base/critical_section.h"
+#include "rtc_base/synchronization/mutex.h"
 #include "rtc_base/thread_annotations.h"
 #include "rtc_base/trace_event.h"
 #include "test/gtest.h"
@@ -20,17 +20,17 @@
 class TestStatistics {
  public:
   void Reset() {
-    rtc::CritScope cs(&crit_);
+    webrtc::MutexLock lock(&mutex_);
     events_logged_ = 0;
   }
 
   void Increment() {
-    rtc::CritScope cs(&crit_);
+    webrtc::MutexLock lock(&mutex_);
     ++events_logged_;
   }
 
   int Count() const {
-    rtc::CritScope cs(&crit_);
+    webrtc::MutexLock lock(&mutex_);
     return events_logged_;
   }
 
@@ -41,8 +41,8 @@
   }
 
  private:
-  rtc::CriticalSection crit_;
-  int events_logged_ RTC_GUARDED_BY(crit_) = 0;
+  mutable webrtc::Mutex mutex_;
+  int events_logged_ RTC_GUARDED_BY(mutex_) = 0;
 };
 
 }  // namespace