Move DevTools out of ash and turn it to a component.

components/ui_devtools/switches.h

 // 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.
 
 #ifndef COMPONENTS_UI_DEVTOOLS_SWITCHES_H_
 #define COMPONENTS_UI_DEVTOOLS_SWITCHES_H_
 
 #include "components/ui_devtools/devtools_export.h"
 
-namespace ui {
-namespace devtools {
+namespace ui_devtools {
 
 extern UI_DEVTOOLS_EXPORT const char kEnableUiDevTools[];
 
-}  // namespace devtools
-}  // namespace ui
+}  // namespace ui_devtools
 
 #endif  // COMPONENTS_UI_DEVTOOLS_SWITCHES_H_