Fix a startup crash from https://crrev.com/5eb3ae10901fa65657abc902910265ab492c5dbf

EasyUnlockKeymanager is not initialized when UpdateEasyUnlockKeys is called
from FinalizePrepareProfile

BUG=419883,422102

Review URL: https://codereview.chromium.org/642153003

Cr-Commit-Position: refs/heads/master@{#299024}

chrome/browser/chromeos/login/session/user_session_manager.cc

@@ -1050,16 +1050,17 @@ void UserSessionManager::UpdateEasyUnlockKeys(const UserContext& user_context) {
         EasyUnlockScreenlockStateHandler::NO_HARDLOCK);
   }
 
+  EasyUnlockKeyManager* key_manager = GetEasyUnlockKeyManager();
   running_easy_unlock_key_ops_ = true;
   if (device_list) {
-    easy_unlock_key_manager_->RefreshKeys(
+    key_manager->RefreshKeys(
         user_context,
         *device_list,
         base::Bind(&UserSessionManager::OnEasyUnlockKeyOpsFinished,
                    AsWeakPtr(),
                    user_context.GetUserID()));
   } else {
-    easy_unlock_key_manager_->RemoveKeys(
+    key_manager->RemoveKeys(
         user_context,
         0,
         base::Bind(&UserSessionManager::OnEasyUnlockKeyOpsFinished,