Move c/b/extension/api/* into extensions namespace

chrome/browser/extensions/api/terminal/terminal_extension_helper.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_EXTENSIONS_API_TERMINAL_TERMINAL_EXTENSION_HELPER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_TERMINAL_TERMINAL_EXTENSION_HELPER_H_
 
 #include <string>
 
 #include "url/gurl.h"
 
 class Profile;
 
+namespace extensions {
+
 class TerminalExtensionHelper {
  public:
   // Returns Hterm extension's entry point for Crosh. If no HTerm extension is
   // installed, returns empty url.
   static GURL GetCroshExtensionURL(Profile* profile);
 };
 
+}  // namespace extensions
+
 #endif  // CHROME_BROWSER_EXTENSIONS_API_TERMINAL_TERMINAL_EXTENSION_HELPER_H_