Do not try to decrypt empty refresh token

chrome/browser/chromeos/settings/device_oauth2_token_service.cc

 // Copyright 2013 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/chromeos/settings/device_oauth2_token_service.h"
 
 #include <string>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 217 matching lines @@
   // If the token has been set meanwhile, write it to |local_state_|.
   if (!refresh_token_.empty()) {
     EncryptAndSaveToken();
     FireRefreshTokensLoaded();
     return;
   }
 
   // Otherwise, load the refresh token from |local_state_|.
   std::string encrypted_refresh_token =
       local_state_->GetString(prefs::kDeviceRobotAnyApiRefreshToken);
-  CryptohomeTokenEncryptor encryptor(system_salt_);
-  refresh_token_ = encryptor.DecryptWithSystemSalt(encrypted_refresh_token);
-  if (!encrypted_refresh_token.empty() && refresh_token_.empty()) {
-    LOG(ERROR) << "Failed to decrypt refresh token.";
-    state_ = STATE_NO_TOKEN;
-    FireRefreshTokensLoaded();
-    return;
+  if (!encrypted_refresh_token.empty()) {
+    CryptohomeTokenEncryptor encryptor(system_salt_);
+    refresh_token_ = encryptor.DecryptWithSystemSalt(encrypted_refresh_token);
+    if (refresh_token_.empty()) {
+      LOG(ERROR) << "Failed to decrypt refresh token.";
+      state_ = STATE_NO_TOKEN;
+      FireRefreshTokensLoaded();
+      return;
+    }
   }
 
   state_ = STATE_VALIDATION_PENDING;
 
   // If there are pending requests, start a validation.
   if (!pending_requests_.empty())
     StartValidation();
 
   // Announce the token.
   FireRefreshTokenAvailable(GetRobotAccountId());
@@ skipping 123 matching lines @@
   GoogleServiceAuthError auth_error(error);
   base::MessageLoop::current()->PostTask(FROM_HERE, base::Bind(
       &RequestImpl::InformConsumer,
       request->AsWeakPtr(),
       auth_error,
       std::string(),
       base::Time()));
 }
 
 }  // namespace chromeos