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diff --git a/base/synchronization/lock_impl.h b/base/synchronization/lock_impl.h
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+++ b/base/synchronization/lock_impl.h
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+// Copyright (c) 2011 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_SYNCHRONIZATION_LOCK_IMPL_H_
+#define BASE_SYNCHRONIZATION_LOCK_IMPL_H_
+#pragma once
+
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include <windows.h>
+#elif defined(OS_POSIX)
+#include <pthread.h>
+#endif
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+
+namespace base {
+namespace internal {
+
+// This class implements the underlying platform-specific spin-lock mechanism
+// used for the Lock class.  Most users should not use LockImpl directly, but
+// should instead use Lock.
+class BASE_EXPORT LockImpl {
+ public:
+#if defined(OS_WIN)
+  typedef CRITICAL_SECTION OSLockType;
+#elif defined(OS_POSIX)
+  typedef pthread_mutex_t OSLockType;
+#endif
+
+  LockImpl();
+  ~LockImpl();
+
+  // If the lock is not held, take it and return true.  If the lock is already
+  // held by something else, immediately return false.
+  bool Try();
+
+  // Take the lock, blocking until it is available if necessary.
+  void Lock();
+
+  // Release the lock.  This must only be called by the lock's holder: after
+  // a successful call to Try, or a call to Lock.
+  void Unlock();
+
+  // Return the native underlying lock.  Not supported for Windows builds.
+  // TODO(awalker): refactor lock and condition variables so that this is
+  // unnecessary.
+#if !defined(OS_WIN)
+  OSLockType* os_lock() { return &os_lock_; }
+#endif
+
+ private:
+  OSLockType os_lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(LockImpl);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_SYNCHRONIZATION_LOCK_IMPL_H_