Add some words of caution to File::Flush().

base/files/file.cc

 // 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.
 
 #include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/files/file_tracing.h"
 #include "base/metrics/histogram.h"
 #include "base/timer/elapsed_timer.h"
 #include "build/build_config.h"
@@ skipping 120 matching lines @@
     case FILE_ERROR_IO:
       return "FILE_ERROR_IO";
     case FILE_ERROR_MAX:
       break;
   }
 
   NOTREACHED();
   return "";
 }
 
-bool File::Flush() {
-  ElapsedTimer timer;
-  SCOPED_FILE_TRACE("Flush");
-  bool return_value = DoFlush();
-  UMA_HISTOGRAM_TIMES("PlatformFile.FlushTime", timer.Elapsed());
-  return return_value;
-}
-
 }  // namespace base