Refactor download image-MIME-type-detection code.

ash/common/system/chromeos/palette/palette_utils.cc

 // Copyright 2016 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 "ash/common/system/chromeos/palette/palette_utils.h"
 
 #include "ash/common/ash_switches.h"
 #include "base/command_line.h"
 
 namespace ash {
 
 bool IsPaletteEnabled() {
   return base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kAshEnablePalette);
 }
 
-}  // namespace chromeos
+}  // namespace ash