Use PlatformThreadId, not int when dealing with thread ids.

base/platform_thread.h

 // Copyright (c) 2006-2008 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.
 
 // WARNING: You should *NOT* be using this class directly.  PlatformThread is
 // the low-level platform-specific abstraction to the OS's threading interface.
 // You should instead be using a message-loop driven Thread, see thread.h.
 
 #ifndef BASE_PLATFORM_THREAD_H_
 #define BASE_PLATFORM_THREAD_H_
 
 #include "base/basictypes.h"
 
 // PlatformThreadHandle should not be assumed to be a numeric type, since the
 // standard intends to allow pthread_t to be a structure.  This means you
 // should not initialize it to a value, like 0.  If it's a member variable, the
 // constructor can safely "value initialize" using () in the initializer list.
 #if defined(OS_WIN)
+#include <windows.h>
+typedef DWORD PlatformThreadId;
 typedef void* PlatformThreadHandle;  // HANDLE
 #elif defined(OS_POSIX)
 #include <pthread.h>
 typedef pthread_t PlatformThreadHandle;
+#if defined(OS_LINUX)
+#include <unistd.h>
+typedef pid_t PlatformThreadId;
+#elif defined(OS_MACOSX)
+#include <mach/mach.h>
+typedef mach_port_t PlatformThreadId;
+#endif
 #endif
 
 // A namespace for low-level thread functions.
 class PlatformThread {
  public:
   // Gets the current thread id, which may be useful for logging purposes.
-  static int CurrentId();
+  static PlatformThreadId CurrentId();
 
   // Yield the current thread so another thread can be scheduled.
   static void YieldCurrentThread();
 
   // Sleeps for the specified duration (units are milliseconds).
   static void Sleep(int duration_ms);
 
   // Sets the thread name visible to a debugger.  This has no effect otherwise.
   static void SetName(const char* name);
 
@@ skipping 20 matching lines @@
   // the caller until the designated thread exits.  This will invalidate
   // |thread_handle|.
   static void Join(PlatformThreadHandle thread_handle);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
 };
 
 #endif  // BASE_PLATFORM_THREAD_H_