Revert 222154 "sync: Gracefully handle very early shutdown"

trunk/src/sync/internal_api/public/base/cancelation_observer.h

-// Copyright 2013 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 SYNC_INTERNAL_API_PUBLIC_BASE_CANCELATION_OBSERVER_H_
-#define SYNC_INTERNAL_API_PUBLIC_BASE_CANCELATION_OBSERVER_H_
-
-#include "sync/base/sync_export.h"
-
-namespace syncer {
-
-// Interface for classes that handle signals from the CancelationSignal.
-class SYNC_EXPORT_PRIVATE CancelationObserver {
- public:
-  CancelationObserver();
-  virtual ~CancelationObserver() = 0;
-
-  // This may be called from a foreign thread while the CancelationSignal's lock
-  // is held.  The callee should avoid performing slow or blocking operations.
-  virtual void OnStopRequested() = 0;
-};
-
-}  // namespace syncer
-
-#endif  // SYNC_INTERNAL_API_PUBLIC_BASE_CANCELATION_OBSERVER_H_