[EasyUnlock] Serialize and store BeaconSeeds along as cryptohome key metadata.

chrome/browser/signin/chrome_proximity_auth_client.cc

 // 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.
 
 #include "chrome/browser/signin/chrome_proximity_auth_client.h"
 
 #include <stdint.h>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 79 matching lines @@
   callback.Run(std::string());
 #endif
 }
 
 PrefService* ChromeProximityAuthClient::GetPrefService() {
   return profile_->GetPrefs();
 }
 
 std::unique_ptr<cryptauth::SecureMessageDelegate>
 ChromeProximityAuthClient::CreateSecureMessageDelegate() {
-  return GetCryptAuthService()->CreateSecureMessageDelegate();
+// Note: Although CryptAuthService::CreateSecureMessageDelegate() exists, we
+// don't use it here (as opposed to other methods in this class) because the
+// CryptAuthService is not available on the ChromeOS login screen.
+#if defined(OS_CHROMEOS)
+  return base::MakeUnique<chromeos::SecureMessageDelegateChromeOS>();
+#else
+  return nullptr;
+#endif
 }
 
 std::unique_ptr<cryptauth::CryptAuthClientFactory>
 ChromeProximityAuthClient::CreateCryptAuthClientFactory() {
   return GetCryptAuthService()->CreateCryptAuthClientFactory();
 }
 
 cryptauth::DeviceClassifier ChromeProximityAuthClient::GetDeviceClassifier() {
   return GetCryptAuthService()->GetDeviceClassifier();
 }
 
 std::string ChromeProximityAuthClient::GetAccountId() {
   return GetCryptAuthService()->GetAccountId();
 }
 
 cryptauth::CryptAuthEnrollmentManager*
 ChromeProximityAuthClient::GetCryptAuthEnrollmentManager() {
   return GetCryptAuthService()->GetCryptAuthEnrollmentManager();
 }
 
 cryptauth::CryptAuthDeviceManager*
 ChromeProximityAuthClient::GetCryptAuthDeviceManager() {
   return GetCryptAuthService()->GetCryptAuthDeviceManager();
 }
 
 cryptauth::CryptAuthService* ChromeProximityAuthClient::GetCryptAuthService() {
   return ChromeCryptAuthServiceFactory::GetInstance()->GetForBrowserContext(
       profile_);
 }