base: Cleanup class/struct forward declarations

base/files/important_file_writer.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 BASE_FILES_IMPORTANT_FILE_WRITER_H_
 #define BASE_FILES_IMPORTANT_FILE_WRITER_H_
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/strings/string_piece.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 
 namespace base {
 
 class SequencedTaskRunner;
-class Thread;
 
 // Helper for atomically writing a file to ensure that it won't be corrupted by
 // *application* crash during write (implemented as create, flush, rename).
 //
 // As an added benefit, ImportantFileWriter makes it less likely that the file
 // is corrupted by *system* crash, though even if the ImportantFileWriter call
 // has already returned at the time of the crash it is not specified which
 // version of the file (old or new) is preserved. And depending on system
 // configuration (hardware and software) a significant likelihood of file
 // corruption may remain, thus using ImportantFileWriter is not a valid
@@ skipping 97 matching lines @@
   const TimeDelta commit_interval_;
 
   WeakPtrFactory<ImportantFileWriter> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ImportantFileWriter);
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_IMPORTANT_FILE_WRITER_H_