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

chrome/browser/extensions/api/downloads_internal/downloads_internal_api.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_DOWNLOADS_INTERNAL_DOWNLOADS_INTERNAL_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_DOWNLOADS_INTERNAL_DOWNLOADS_INTERNAL_API_H_
 
 #include "chrome/browser/extensions/extension_function.h"
 
+namespace extensions {
+
 class DownloadsInternalDetermineFilenameFunction
     : public AsyncExtensionFunction {
  public:
   DECLARE_EXTENSION_FUNCTION("downloadsInternal.determineFilename",
                              DOWNLOADSINTERNAL_DETERMINEFILENAME);
   DownloadsInternalDetermineFilenameFunction();
   virtual bool RunImpl() OVERRIDE;
 
  protected:
   virtual ~DownloadsInternalDetermineFilenameFunction();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DownloadsInternalDetermineFilenameFunction);
 };
 
+}  // namespace extensions
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DOWNLOADS_INTERNAL_DOWNLOADS_INTERNAL_API_H_