chrome: Cleanup class/struct forward declarations

chrome/browser/chromeos/extensions/wallpaper_private_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_CHROMEOS_EXTENSIONS_WALLPAPER_PRIVATE_API_H_
 #define CHROME_BROWSER_CHROMEOS_EXTENSIONS_WALLPAPER_PRIVATE_API_H_
 
 #include <string>
 #include <vector>
 
 #include "chrome/browser/chromeos/extensions/wallpaper_function_base.h"
 #include "chrome/common/extensions/api/wallpaper_private.h"
 #include "components/signin/core/account_id/account_id.h"
 #include "components/wallpaper/wallpaper_files_id.h"
 #include "net/url_request/url_fetcher_delegate.h"
 
 namespace base {
 class RefCountedBytes;
 }
 
-namespace chromeos {
-class UserImage;
-}  // namespace chromeos
-
 // Wallpaper manager strings.
 class WallpaperPrivateGetStringsFunction : public UIThreadExtensionFunction {
  public:
   DECLARE_EXTENSION_FUNCTION("wallpaperPrivate.getStrings",
                              WALLPAPERPRIVATE_GETSTRINGS)
 
  protected:
   ~WallpaperPrivateGetStringsFunction() override {}
 
   // ExtensionFunction:
@@ skipping 256 matching lines @@
                              WALLPAPERPRIVATE_RECORDWALLPAPERUMA)
 
  protected:
   ~WallpaperPrivateRecordWallpaperUMAFunction() override {}
 
   // ExtensionFunction:
   ResponseAction Run() override;
 };
 
 #endif  // CHROME_BROWSER_CHROMEOS_EXTENSIONS_WALLPAPER_PRIVATE_API_H_