Remove mutable from rtc::CriticalSection members.

rtc::CriticalSection is now lockable from const methods and no longer
need to remain mutable.

BUG=
R=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1613643004

Cr-Commit-Position: refs/heads/master@{#11367}
diff --git a/webrtc/call/bitrate_allocator.h b/webrtc/call/bitrate_allocator.h
index 88a9960..5028e12 100644
--- a/webrtc/call/bitrate_allocator.h
+++ b/webrtc/call/bitrate_allocator.h
@@ -89,7 +89,7 @@
   ObserverBitrateMap LowRateAllocation(uint32_t bitrate)
       EXCLUSIVE_LOCKS_REQUIRED(crit_sect_);
 
-  mutable rtc::CriticalSection crit_sect_;
+  rtc::CriticalSection crit_sect_;
   // Stored in a list to keep track of the insertion order.
   BitrateObserverConfList bitrate_observers_ GUARDED_BY(crit_sect_);
   bool bitrate_observers_modified_ GUARDED_BY(crit_sect_);
diff --git a/webrtc/call/call_perf_tests.cc b/webrtc/call/call_perf_tests.cc
index fa81953..3ee49d9 100644
--- a/webrtc/call/call_perf_tests.cc
+++ b/webrtc/call/call_perf_tests.cc
@@ -113,7 +113,7 @@
     ntp_rtp_pairs_.push_front(ntp_rtp_pair);
   }
 
-  mutable rtc::CriticalSection crit_;
+  rtc::CriticalSection crit_;
   RtcpList ntp_rtp_pairs_ GUARDED_BY(crit_);
 };
 
diff --git a/webrtc/call/congestion_controller.h b/webrtc/call/congestion_controller.h
index b77c46f..5f5e590 100644
--- a/webrtc/call/congestion_controller.h
+++ b/webrtc/call/congestion_controller.h
@@ -74,7 +74,7 @@
   rtc::scoped_ptr<RemoteBitrateEstimator> remote_bitrate_estimator_;
   rtc::scoped_ptr<RemoteEstimatorProxy> remote_estimator_proxy_;
 
-  mutable rtc::CriticalSection encoder_crit_;
+  rtc::CriticalSection encoder_crit_;
   std::vector<ViEEncoder*> encoders_ GUARDED_BY(encoder_crit_);
 
   // Registered at construct time and assumed to outlive this class.