ListAccounts will return the Gaia ID as well as the email of the account.

chrome/browser/signin/cross_device_promo.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 CHROME_BROWSER_SIGNIN_CROSS_DEVICE_PROMO_H_
 #define CHROME_BROWSER_SIGNIN_CROSS_DEVICE_PROMO_H_
 
 #include "base/observer_list.h"
 #include "base/timer/timer.h"
 #include "components/keyed_service/core/keyed_service.h"
@@ skipping 26 matching lines @@
   ~CrossDevicePromo() override;
 
   // KeyedService:
   void Shutdown() override;
 
   void AddObserver(CrossDevicePromo::Observer* observer);
   void RemoveObserver(CrossDevicePromo::Observer* observer);
 
   // GaiaCookieManagerService::Observer:
   void OnGaiaAccountsInCookieUpdated(
-      const std::vector<std::pair<std::string, bool>>& accounts,
+      const std::vector<gaia::ListedAccount>& accounts,
       const GoogleServiceAuthError& error) override;
 
   // DeviceActivityFetcher::Observer:
   void OnFetchDeviceActivitySuccess(
       const std::vector<DeviceActivityFetcher::DeviceActivity>& devices)
       override;
   void OnFetchDeviceActivityFailure() override;
 
   // Profile should be shown the promo.
   bool IsPromoActive();
@@ skipping 72 matching lines @@
   // configurigng the promo.
   base::Time start_last_browsing_session_;
 
   // Used to delay the check of Device Activity.
   base::OneShotTimer<CrossDevicePromo> device_activity_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(CrossDevicePromo);
 };
 
 #endif  // CHROME_BROWSER_SIGNIN_CROSS_DEVICE_PROMO_H_