Expose signing key from cloud policy stores

chrome/browser/chromeos/policy/user_cloud_policy_store_chromeos.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_POLICY_USER_CLOUD_POLICY_STORE_CHROMEOS_H_
 #define CHROME_BROWSER_CHROMEOS_POLICY_USER_CLOUD_POLICY_STORE_CHROMEOS_H_
 
 #include <memory>
 #include <string>
 #include <vector>
@@ skipping 118 matching lines @@
   base::FilePath user_policy_key_dir_;
 
   // TODO(mnissler): Remove all the legacy policy support members below after
   // the number of pre-M20 clients drops back to zero.
   base::FilePath legacy_cache_dir_;
   std::unique_ptr<LegacyPolicyCacheLoader> legacy_loader_;
   bool legacy_caches_loaded_;
 
   bool policy_key_loaded_;
   base::FilePath policy_key_path_;
-  std::string policy_key_;
 
   base::WeakPtrFactory<UserCloudPolicyStoreChromeOS> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UserCloudPolicyStoreChromeOS);
 };
 
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_CHROMEOS_POLICY_USER_CLOUD_POLICY_STORE_CHROMEOS_H_