[EasyUnlock] Put entire ChromeOS login flow behind a flag.

components/proximity_auth/switches.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 "components/proximity_auth/switches.h"
 
 namespace proximity_auth {
 namespace switches {
 
 // Enables discovery of the phone over Bluetooth Low Energy.
 const char kEnableBluetoothLowEnergyDiscovery[] =
     "enable-proximity-auth-bluetooth-low-energy-discovery";
 
+// Enables the use of EasyUnlock to log into the Chromebook.
+extern const char kEnableChromeOSLogin[] =
+    "enable-proximity-auth-chromeos-login";
+
 // Enables close proximity detection. This allows the user to set a setting to
 // require very close proximity between the remote device and the local device
 // in order to unlock the local device, which trades off convenience for
 // security.
 const char kEnableProximityDetection[] =
     "enable-proximity-auth-proximity-detection";
 
 // Force easy unlock app loading in test.
 // TODO(xiyuan): Remove this when app could be bundled with Chrome.
 const char kForceLoadEasyUnlockAppInTests[] =
     "force-load-easy-unlock-app-in-tests";
 
 }  // namespace switches
 }  // namespace proximity_auth