Make CreateDirectory consistent on Win and Posix when directory exists.

base/file_util.h

 // Copyright (c) 2006-2008 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 contains utility functions for dealing with the local
 // filesystem.
 
 #ifndef BASE_FILE_UTIL_H_
 #define BASE_FILE_UTIL_H_
 
@@ skipping 204 matching lines @@
 // TODO(erikkay): rename this function and track down all of the callers.
 bool CreateTemporaryFileName(std::wstring* temp_file);
 
 // Create a new directory under TempPath. If prefix is provided, the new
 // directory name is in the format of prefixyyyy.
 // If success, return true and output the full path of the directory created.
 bool CreateNewTempDirectory(const std::wstring& prefix,
                             std::wstring* new_temp_path);
 
 // Creates a directory, as well as creating any parent directories, if they
-// don't exist. Returns 'true' on successful creation.
+// don't exist. Returns 'true' on successful creation, or if the directory
+// already exists.
 bool CreateDirectory(const std::wstring& full_path);
 
 // Returns the file size. Returns true on success.
 bool GetFileSize(const std::wstring& file_path, int64* file_size);
 
 // Reads the given number of bytes from the file into the buffer.  Returns
 // the number of read bytes, or -1 on error.
 int ReadFile(const std::wstring& filename, char* data, int size);
 
 // Writes the given buffer into the file, overwriting any data that was
@@ skipping 77 matching lines @@
 
 // Renames a file using the MoveFileEx API and ensures that the target file gets
 // the correct security descriptor in the new path.
 bool RenameFileAndResetSecurityDescriptor(
     const std::wstring& source_file_path,
     const std::wstring& target_file_path);
 
 }  // namespace file_util
 
 #endif  // BASE_FILE_UTIL_H_
-