[Sync] Remove backend unrecoverable error handler

sync/util/test_unrecoverable_error_handler.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 SYNC_INTERNAL_API_INCLUDES_TEST_UNRECOVERABLE_ERROR_HANDLER_H_
 #define SYNC_INTERNAL_API_INCLUDES_TEST_UNRECOVERABLE_ERROR_HANDLER_H_
 
 #include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
 #include "sync/internal_api/public/util/unrecoverable_error_handler.h"
 
 namespace syncer {
 
 // Implementation of UnrecoverableErrorHandler that simply adds a
 // gtest failure.
 class TestUnrecoverableErrorHandler : public UnrecoverableErrorHandler {
  public:
   TestUnrecoverableErrorHandler();
   ~TestUnrecoverableErrorHandler() override;
 
   void OnUnrecoverableError(const tracked_objects::Location& from_here,
                             const std::string& message) override;
+
+  base::WeakPtr<TestUnrecoverableErrorHandler> GetWeakPtr();
+
+ private:
+  base::WeakPtrFactory<TestUnrecoverableErrorHandler> weak_ptr_factory_;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_INCLUDES_TEST_UNRECOVERABLE_ERROR_HANDLER_H_