Use queue label as id in SequencedTaskChecker when not running on TaskQueue

webrtc/base/sequenced_task_checker_impl.h

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 16 matching lines @@
   ~SequencedTaskCheckerImpl();
 
   bool CalledSequentially() const;
 
   // Changes the task queue or thread that is checked for in IsCurrent.  This
   // may be useful when an object may be created on one task queue / thread and
   // then used exclusively on another thread.
   void Detach();
 
  private:
+  typedef const void* QueueId;
   CriticalSection lock_;
   ThreadChecker thread_checker_;
   mutable bool attached_;
-  mutable TaskQueue* valid_queue_;
+  mutable QueueId valid_queue_;
 };
 
 }  // namespace rtc
 #endif  // WEBRTC_BASE_SEQUENCED_TASK_CHECKER_IMPL_H_