Render base::File::Flush() doc more precise.

base/files/file.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_FILE_H_
 #define BASE_FILES_FILE_H_
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
 #include <windows.h>
@@ skipping 231 matching lines @@
   int WriteAtCurrentPosNoBestEffort(const char* data, int size);
 
   // Returns the current size of this file, or a negative number on failure.
   int64 GetLength();
 
   // Truncates the file to the given length. If |length| is greater than the
   // current size of the file, the file is extended with zeros. If the file
   // doesn't exist, |false| is returned.
   bool SetLength(int64 length);
 
-  // Flushes the buffers.
+  // Instructs the filesystem to flush the file to disk. (POSIX: fsync, Windows:
+  // FlushFileBuffers).
   bool Flush();
 
   // Updates the file times.
   bool SetTimes(Time last_access_time, Time last_modified_time);
 
   // Returns some basic information for the given file.
   bool GetInfo(Info* info);
 
   // Attempts to take an exclusive write lock on the file. Returns immediately
   // (i.e. does not wait for another process to unlock the file). If the lock
@@ skipping 41 matching lines @@
 #endif
 
   Error error_details_;
   bool created_;
   bool async_;
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_H_