Disable PIN unlock in m53.

chrome/browser/chromeos/login/quick_unlock/pin_storage.cc

 // Copyright 2016 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/quick_unlock/pin_storage.h"
 
 #include "base/base64.h"
 #include "base/strings/string_util.h"
 #include "chrome/common/pref_names.h"
 #include "chromeos/login/auth/key.h"
@@ skipping 86 matching lines @@
 
 std::string PinStorage::PinSalt() const {
   return pref_service_->GetString(prefs::kQuickUnlockPinSalt);
 }
 
 std::string PinStorage::PinSecret() const {
   return pref_service_->GetString(prefs::kQuickUnlockPinSecret);
 }
 
 bool PinStorage::IsPinAuthenticationAvailable() const {
-  return IsPinSet() && unlock_attempt_count() < kMaximumUnlockAttempts &&
-         HasStrongAuth() && TimeSinceLastStrongAuth() < kStrongAuthTimeout;
+  return false;
 }
 
 bool PinStorage::TryAuthenticatePin(const std::string& pin) {
   if (!IsPinAuthenticationAvailable())
     return false;
 
   AddUnlockAttempt();
   return ComputeSecret(pin, PinSalt()) == PinSecret();
 }
 
 }  // namespace chromeos