startup: Put it in chrome namespace.

chrome/browser/ui/startup/obsolete_os_prompt.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.
 
 #ifndef CHROME_BROWSER_UI_STARTUP_OBSOLETE_OS_PROMPT_H_
 #define CHROME_BROWSER_UI_STARTUP_OBSOLETE_OS_PROMPT_H_
 #pragma once
 
 #include "build/build_config.h"
 
 class Browser;
 class PrefService;
 
-namespace browser {
+namespace chrome {
 
 #if defined(OS_MACOSX)
-// Registers the Mac-specific preference about when to show obsolete OS
-// prompts.
+// Registers the Mac-specific preference about when to show obsolete OS prompts.
 void RegisterObsoleteOSInfobarPrefs(PrefService* local_state);
 #endif
 
 // Shows a warning notification in |browser| that the app is being run on an
 // unsupported operating system.
 void ShowObsoleteOSPrompt(Browser* browser);
 
-}  // namespace browser
+}  // namespace chrome
 
 #endif  // CHROME_BROWSER_UI_STARTUP_OBSOLETE_OS_PROMPT_H_