Linux: Move base/mime_util* to base/nix. It's not used on any other platform.

base/nix/mime_util_xdg.h

 // 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.
 
-#ifndef BASE_MIME_UTIL_H_
-#define BASE_MIME_UTIL_H_
+#ifndef BASE_NIX_MIME_UTIL_XDG_H_
+#define BASE_NIX_MIME_UTIL_XDG_H_
 #pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 #include "build/build_config.h"
 
 class FilePath;
 
-namespace mime_util {
+namespace base {
+namespace nix {
 
 // Gets the mime type for a file based on its filename. The file path does not
 // have to exist. Please note because it doesn't touch the disk, this does not
 // work for directories.
 // If the mime type is unknown, this will return application/octet-stream.
 BASE_EXPORT std::string GetFileMimeType(const FilePath& filepath);
 
 // Get the mime type for a byte vector.
 BASE_EXPORT std::string GetDataMimeType(const std::string& data);
 
 #if defined(TOOLKIT_USES_GTK)
 // This detects the current GTK theme by calling gtk_settings_get_default().
 // It should only be executed on the UI thread and must be called before
 // GetMimeIcon().
 BASE_EXPORT void DetectGtkTheme();
 #endif
 
 // Gets the file name for an icon given the mime type and icon pixel size.
 // Where an icon is a square image of |size| x |size|.
 // This will try to find the closest matching icon. If that's not available,
 // then a generic icon, and finally an empty FilePath if all else fails.
 BASE_EXPORT FilePath GetMimeIcon(const std::string& mime_type, size_t size);
 
-}  // namespace mime_util
+}  // namespace nix
+}  // namespace base
 
-#endif  // BASE_MIME_UTIL_H_
+#endif  // BASE_NIX_MIME_UTIL_XDG_H_