Re-enable Thread::Stop() sequence checks and consequently remove |thread_lock|.

base/threading/thread.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_THREADING_THREAD_H_
 #define BASE_THREADING_THREAD_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 246 matching lines @@
   // Should be written on the thread that created this thread. Also read data
   // could be wrong on other threads.
   bool stopping_ = false;
 
   // True while inside of Run().
   bool running_ = false;
   mutable base::Lock running_lock_;  // Protects |running_|.
 
   // The thread's handle.
   PlatformThreadHandle thread_;
-  mutable base::Lock thread_lock_;  // Protects |thread_|.
 
   // The thread's id once it has started.
   PlatformThreadId id_ = kInvalidThreadId;
   mutable WaitableEvent id_event_;  // Protects |id_|.
 
   // The thread's MessageLoop and RunLoop. Valid only while the thread is alive.
   // Set by the created thread.
   MessageLoop* message_loop_ = nullptr;
   RunLoop* run_loop_ = nullptr;
 
@@ skipping 10 matching lines @@
   // This class is not thread-safe, use this to verify access from the owning
   // sequence of the Thread.
   SequenceChecker owning_sequence_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_H_