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

chrome/browser/chromeos/login/signin/oauth2_login_manager.cc

 // 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.
 
 #include "chrome/browser/chromeos/login/signin/oauth2_login_manager.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 289 matching lines @@
 void OAuth2LoginManager::OnSessionMergeFailure(bool connection_error) {
   LOG(ERROR) << "OAuth2 refresh and GAIA token verification failed!"
              << " connection_error: " << connection_error;
   RecordSessionRestoreOutcome(SESSION_RESTORE_MERGE_SESSION_FAILED,
                               connection_error ?
                                   SESSION_RESTORE_CONNECTION_FAILED :
                                   SESSION_RESTORE_FAILED);
 }
 
 void OAuth2LoginManager::OnListAccountsSuccess(
-    const std::vector<std::pair<std::string, bool>>& accounts) {
+    const std::vector<gaia::ListedAccount>& accounts) {
   MergeVerificationOutcome outcome = POST_MERGE_SUCCESS;
   // Let's analyze which accounts we see logged in here:
   std::string user_email = gaia::CanonicalizeEmail(GetPrimaryAccountId());
   if (!accounts.empty()) {
     bool found = false;
     bool first = true;
-    for (std::vector<std::pair<std::string, bool> >::const_iterator iter =
+    for (std::vector<gaia::ListedAccount>::const_iterator iter =
              accounts.begin();
          iter != accounts.end(); ++iter) {
-      if (gaia::CanonicalizeEmail(iter->first) == user_email) {
-        found = iter->second;
+      if (gaia::CanonicalizeEmail(iter->email) == user_email) {

[xiyuan, 2015/06/04 15:59:24]

nit: |email| is canonicalized so we probably can remove CanonicalizeEmail call
here.

[Mike Lerman, 2015/06/04 16:52:41]

Done.

+        found = iter->valid;
         break;
       }
 
       first = false;
     }
 
     if (!found)
       outcome = POST_MERGE_MISSING_PRIMARY_ACCOUNT;
     else if (!first)
       outcome = POST_MERGE_PRIMARY_NOT_FIRST_ACCOUNT;
@@ skipping 77 matching lines @@
   FOR_EACH_OBSERVER(Observer, observer_list_,
                     OnSessionRestoreStateChanged(user_profile_, state_));
 }
 
 void OAuth2LoginManager::SetSessionRestoreStartForTesting(
     const base::Time& time) {
   session_restore_start_ = time;
 }
 
 }  // namespace chromeos