Added check for valid account cookies in /ListAccounts result processing.

BUG=414956
TEST=manual

Review URL: https://codereview.chromium.org/551373009

Cr-Commit-Position: refs/heads/master@{#295208}

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

@@ -312,7 +312,7 @@ void OAuth2LoginManager::OnListAccountsSuccess(const std::string& data) {
              accounts.begin();
          iter != accounts.end(); ++iter) {
       if (gaia::CanonicalizeEmail(iter->first) == user_email) {
-        found = true;
+        found = iter->second;
         break;
       }