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.cc b/modules/video_coding/generic_decoder.cc
index cfe16ed..50ecd8d 100644
--- a/modules/video_coding/generic_decoder.cc
+++ b/modules/video_coding/generic_decoder.cc
@@ -86,7 +86,7 @@
   // callbacks from one call to Decode().
   VCMFrameInformation* frameInfo;
   {
-    rtc::CritScope cs(&lock_);
+    MutexLock lock(&lock_);
     frameInfo = _timestampMap.Pop(decodedImage.timestamp());
   }
 
@@ -172,12 +172,12 @@
 
 void VCMDecodedFrameCallback::Map(uint32_t timestamp,
                                   VCMFrameInformation* frameInfo) {
-  rtc::CritScope cs(&lock_);
+  MutexLock lock(&lock_);
   _timestampMap.Add(timestamp, frameInfo);
 }
 
 int32_t VCMDecodedFrameCallback::Pop(uint32_t timestamp) {
-  rtc::CritScope cs(&lock_);
+  MutexLock lock(&lock_);
   if (_timestampMap.Pop(timestamp) == NULL) {
     return VCM_GENERAL_ERROR;
   }