components: Cleanup class/struct fwd declarations

components/signin/core/browser/signin_client.h

 // Copyright 2014 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_SIGNIN_CORE_BROWSER_SIGNIN_CLIENT_H_
 #define COMPONENTS_SIGNIN_CORE_BROWSER_SIGNIN_CLIENT_H_
 
 #include "base/callback.h"
 #include "base/callback_list.h"
 #include "base/time/time.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/signin/core/browser/account_info.h"
 #include "components/signin/core/browser/webdata/token_web_data.h"
 #include "google_apis/gaia/gaia_auth_fetcher.h"
 #include "net/cookies/cookie_store.h"
 #include "url/gurl.h"
 
 class PrefService;
-class SigninManagerBase;
 class TokenWebData;
 
 namespace content_settings {
 class Observer;
 }
 
 namespace net {
 class URLRequestContextGetter;
 }
 
@@ skipping 104 matching lines @@
 
  private:
   // Perform Chrome-specific sign out. This happens when user signs out or about
   // to sign in.
   // This method should not be called from the outside of SigninClient. External
   // callers must use SignOut() instead.
   virtual void OnSignedOut() = 0;
 };
 
 #endif  // COMPONENTS_SIGNIN_CORE_BROWSER_SIGNIN_CLIENT_H_