Reland of Reimplement AccountManagerHelper singleton instance creation

components/signin/core/browser/child_account_info_fetcher.h

 // Copyright 2015 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_CHILD_ACCOUNT_INFO_FETCHER_H_
 #define COMPONENTS_SIGNIN_CORE_BROWSER_CHILD_ACCOUNT_INFO_FETCHER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 16 matching lines @@
  public:
   // Caller takes ownership of the fetcher and keeps it alive in order to
   // receive updates.
   static std::unique_ptr<ChildAccountInfoFetcher> CreateFrom(
       const std::string& account_id,
       AccountFetcherService* fetcher_service,
       OAuth2TokenService* token_service,
       net::URLRequestContextGetter* request_context_getter,
       invalidation::InvalidationService* invalidation_service);
   virtual ~ChildAccountInfoFetcher();
+
+  static void InitializeForTests();
 };
 
 #endif  // COMPONENTS_SIGNIN_CORE_BROWSER_CHILD_ACCOUNT_INFO_FETCHER_H_