Transform ImagePreReader into PreReadFile.

chrome/app/file_pre_reader_win.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.
+
+// This file defines a function to pre-read a file in order to avoid touching
+// the disk when it is subsequently used.
+
+#ifndef CHROME_APP_FILE_PRE_READER_WIN_H_
+#define CHROME_APP_FILE_PRE_READER_WIN_H_
+
+namespace base {
+class FilePath;
+}
+
+// Reads |file_path| to avoid touching the disk when the file is actually used.
+// The function checks the Windows version to determine which pre-reading
+// mechanism to use. On Vista+, chunks of |step_size| bytes are read into a
+// buffer. The bigger |step_size| is, the faster the file is pre-read (up to
+// about 4MB according to local tests), but also the more memory is allocated
+// for the buffer. On XP, pre-reading non-PE files is not supported.
+bool PreReadFile(const base::FilePath& file_path, int step_size);
+
+#endif  // CHROME_APP_FILE_PRE_READER_WIN_H_