Remove mutable from rtc::CriticalSection members.

webrtc/test/fake_network_pipe.h

Index: webrtc/test/fake_network_pipe.h
diff --git a/webrtc/test/fake_network_pipe.h b/webrtc/test/fake_network_pipe.h
index 5d589d86f049a486f8f8e47c7fc618f197384692..99c5c1366bc3038e7aafe9d276fc14c69195d0f3 100644
--- a/webrtc/test/fake_network_pipe.h
+++ b/webrtc/test/fake_network_pipe.h
@@ -71,7 +71,7 @@ class FakeNetworkPipe {
 
  private:
   Clock* const clock_;
-  mutable rtc::CriticalSection lock_;
+  rtc::CriticalSection lock_;
   PacketReceiver* packet_receiver_;
   std::queue<NetworkPacket*> capacity_link_;
   std::queue<NetworkPacket*> delay_link_;