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

chrome/browser/chromeos/login/signin/oauth2_login_verifier.h

 // Copyright 2014 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_LOGIN_SIGNIN_OAUTH2_LOGIN_VERIFIER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SIGNIN_OAUTH2_LOGIN_VERIFIER_H_
 
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 14 matching lines @@
     virtual ~Delegate() {}
     // Invoked when cookie session is successfully merged.
     virtual void OnSessionMergeSuccess() = 0;
 
     // Invoked when cookie session can not be merged.
     virtual void OnSessionMergeFailure(bool connection_error) = 0;
 
     // Invoked when account list is retrieved during post-merge session
     // verification.
     virtual void OnListAccountsSuccess(
-        const std::vector<std::pair<std::string, bool>>& accounts) = 0;
+        const std::vector<gaia::ListedAccount>& accounts) = 0;
 
     // Invoked when post-merge session verification fails.
     virtual void OnListAccountsFailure(bool connection_error) = 0;
   };
 
   OAuth2LoginVerifier(OAuth2LoginVerifier::Delegate* delegate,
                       GaiaCookieManagerService* cookie_manager_service,
                       const std::string& primary_account_id,
                       const std::string& oauthlogin_access_token);
   ~OAuth2LoginVerifier() override;
 
   // Initiates verification of GAIA cookies in |profile|'s cookie jar.
   void VerifyUserCookies(Profile* profile);
 
   // Attempts to restore session from OAuth2 refresh token minting all necessary
   // tokens along the way (OAuth2 access token, SID/LSID, GAIA service token).
   void VerifyProfileTokens(Profile* profile);
 
  private:
   // GaiaCookieManagerService::Observer
   void OnAddAccountToCookieCompleted(
       const std::string& account_id,
       const GoogleServiceAuthError& error) override;
   void OnGaiaAccountsInCookieUpdated(
-        const std::vector<std::pair<std::string, bool> >& accounts,
-        const GoogleServiceAuthError& error) override;
+      const std::vector<gaia::ListedAccount>& accounts,
+      const GoogleServiceAuthError& error) override;
 
   OAuth2LoginVerifier::Delegate* delegate_;
   GaiaCookieManagerService* cookie_manager_service_;
   const std::string& primary_account_id_;
   const std::string access_token_;
 
   DISALLOW_COPY_AND_ASSIGN(OAuth2LoginVerifier);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SIGNIN_OAUTH2_LOGIN_VERIFIER_H_