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/base/bufferqueue.h b/webrtc/base/bufferqueue.h
index 458f018..89ffdf0 100644
--- a/webrtc/base/bufferqueue.h
+++ b/webrtc/base/bufferqueue.h
@@ -45,7 +45,7 @@
  private:
   size_t capacity_;
   size_t default_size_;
-  mutable CriticalSection crit_;
+  CriticalSection crit_;
   std::deque<Buffer*> queue_ GUARDED_BY(crit_);
   std::vector<Buffer*> free_list_ GUARDED_BY(crit_);
 
diff --git a/webrtc/base/messagequeue.h b/webrtc/base/messagequeue.h
index c3ab3b6..856a6eb 100644
--- a/webrtc/base/messagequeue.h
+++ b/webrtc/base/messagequeue.h
@@ -251,7 +251,7 @@
   MessageList msgq_;
   PriorityQueue dmsgq_;
   uint32_t dmsgq_next_num_;
-  mutable CriticalSection crit_;
+  CriticalSection crit_;
 
  private:
   RTC_DISALLOW_COPY_AND_ASSIGN(MessageQueue);
diff --git a/webrtc/base/physicalsocketserver.h b/webrtc/base/physicalsocketserver.h
index ae1f10f..cbe6580 100644
--- a/webrtc/base/physicalsocketserver.h
+++ b/webrtc/base/physicalsocketserver.h
@@ -172,7 +172,7 @@
   SOCKET s_;
   uint8_t enabled_events_;
   bool udp_;
-  mutable CriticalSection crit_;
+  CriticalSection crit_;
   int error_ GUARDED_BY(crit_);
   ConnState state_;
   AsyncResolver* resolver_;
diff --git a/webrtc/base/stream.h b/webrtc/base/stream.h
index c57daae..98123b8 100644
--- a/webrtc/base/stream.h
+++ b/webrtc/base/stream.h
@@ -555,7 +555,7 @@
   size_t data_length_;  // amount of readable data in the buffer
   size_t read_position_;  // offset to the readable data
   Thread* owner_;  // stream callbacks are dispatched on this thread
-  mutable CriticalSection crit_;  // object lock
+  CriticalSection crit_;  // object lock
   RTC_DISALLOW_COPY_AND_ASSIGN(FifoBuffer);
 };
 
diff --git a/webrtc/base/thread_checker_impl.h b/webrtc/base/thread_checker_impl.h
index 0455835..b9867c3 100644
--- a/webrtc/base/thread_checker_impl.h
+++ b/webrtc/base/thread_checker_impl.h
@@ -37,7 +37,7 @@
   void DetachFromThread();
 
  private:
-  mutable CriticalSection lock_;
+  CriticalSection lock_;
   // This is mutable so that CalledOnValidThread can set it.
   // It's guarded by |lock_|.
   mutable PlatformThreadRef valid_thread_;
diff --git a/webrtc/base/thread_unittest.cc b/webrtc/base/thread_unittest.cc
index 7ed4326..240ffc4 100644
--- a/webrtc/base/thread_unittest.cc
+++ b/webrtc/base/thread_unittest.cc
@@ -164,7 +164,7 @@
   }
 
  private:
-  mutable CriticalSection cs_;
+  CriticalSection cs_;
   bool flag_;
 };