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/generic_decoder_unittest.cc b/modules/video_coding/generic_decoder_unittest.cc
index 3e07a2a..dbceb18 100644
--- a/modules/video_coding/generic_decoder_unittest.cc
+++ b/modules/video_coding/generic_decoder_unittest.cc
@@ -16,8 +16,8 @@
 #include "api/task_queue/default_task_queue_factory.h"
 #include "common_video/test/utilities.h"
 #include "modules/video_coding/timing.h"
-#include "rtc_base/critical_section.h"
 #include "rtc_base/event.h"
+#include "rtc_base/synchronization/mutex.h"
 #include "system_wrappers/include/clock.h"
 #include "test/fake_decoder.h"
 #include "test/gmock.h"
@@ -33,7 +33,7 @@
                         int32_t decode_time_ms,
                         VideoContentType content_type) override {
     {
-      rtc::CritScope cs(&lock_);
+      MutexLock lock(&lock_);
       last_frame_ = videoFrame;
     }
     received_frame_event_.Set();
@@ -41,13 +41,13 @@
   }
 
   absl::optional<VideoFrame> GetLastFrame() {
-    rtc::CritScope cs(&lock_);
+    MutexLock lock(&lock_);
     return last_frame_;
   }
 
   absl::optional<VideoFrame> WaitForFrame(int64_t wait_ms) {
     if (received_frame_event_.Wait(wait_ms)) {
-      rtc::CritScope cs(&lock_);
+      MutexLock lock(&lock_);
       return last_frame_;
     } else {
       return absl::nullopt;
@@ -55,7 +55,7 @@
   }
 
  private:
-  rtc::CriticalSection lock_;
+  Mutex lock_;
   rtc::Event received_frame_event_;
   absl::optional<VideoFrame> last_frame_ RTC_GUARDED_BY(lock_);
 };