Use PlatformThreadId, not int when dealing with thread ids.

base/thread_collision_warner.h

 // Copyright (c) 2008 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 THREAD_COLLISION_WARNER_H_
 #define THREAD_COLLISION_WARNER_H_
 
 #include <memory>
 
 #include "base/atomicops.h"
@@ skipping 207 matching lines @@
 
   // Same as EnterSelf but recursion is not allowed.
   void Enter();
 
   // Removes the thread_id stored in order to allow other threads to
   // call EnterSelf or Enter.
   void Leave();
 
   // This stores the thread id that is inside the critical section, if the 
   // value is 0 then no thread is inside.
-  volatile int valid_thread_id_;
+  volatile subtle::Atomic32 valid_thread_id_;
 
   // Counter to trace how many time a critical section was "pinned"
   // (when allowed) in order to unpin it when counter_ reaches 0.
   volatile subtle::Atomic32 counter_;
 
   // Here only for class unit tests purpose, during the test I need to not
   // DCHECK but notify the collision with something else.
   AsserterBase* asserter_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadCollisionWarner);
 };
 
 }  // namespace base
 
 #endif  // THREAD_COLLISION_WARNER_H_