Replaced CriticalSectionWrapper with rtc::CriticalSection in rtp_rtcp module

Review URL: https://codereview.webrtc.org/1877253002

Cr-Commit-Position: refs/heads/master@{#12359}
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index 5875529..64f64d8 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -112,7 +112,6 @@
       key_frame_req_method_(kKeyFrameReqPliRtcp),
       remote_bitrate_(configuration.remote_bitrate_estimator),
       rtt_stats_(configuration.rtt_stats),
-      critical_section_rtt_(CriticalSectionWrapper::CreateCriticalSection()),
       rtt_ms_(0) {
   // Make sure that RTCP objects are aware of our SSRC.
   uint32_t SSRC = rtp_sender_.SSRC();
@@ -982,12 +981,12 @@
 }
 
 void ModuleRtpRtcpImpl::set_rtt_ms(int64_t rtt_ms) {
-  CriticalSectionScoped cs(critical_section_rtt_.get());
+  rtc::CritScope cs(&critical_section_rtt_);
   rtt_ms_ = rtt_ms;
 }
 
 int64_t ModuleRtpRtcpImpl::rtt_ms() const {
-  CriticalSectionScoped cs(critical_section_rtt_.get());
+  rtc::CritScope cs(&critical_section_rtt_);
   return rtt_ms_;
 }