Remove mutable from rtc::CriticalSection members.

webrtc/call/bitrate_allocator.h

Index: webrtc/call/bitrate_allocator.h
diff --git a/webrtc/call/bitrate_allocator.h b/webrtc/call/bitrate_allocator.h
index 88a9960f1f6b1f31d5ee81ed83d47e7fab541514..5028e124bdfc0f1463669d6e665587182948f816 100644
--- a/webrtc/call/bitrate_allocator.h
+++ b/webrtc/call/bitrate_allocator.h
@@ -89,7 +89,7 @@ class BitrateAllocator {
   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_);