[Smart Lock] Add a setting to require close proximity in order for unlocking to work.

chrome/common/pref_names.h

 // Copyright (c) 2012 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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 
 #include <stddef.h>
@@ skipping 381 matching lines @@
 
 extern const char kFullscreenAllowed[];
 
 extern const char kLocalDiscoveryNotificationsEnabled[];
 
 extern const char kPreferenceResetTime[];
 
 extern const char kGCMChannelEnabled[];
 extern const char kPushMessagingRegistrationCount[];
 
+extern const char kEasyUnlockAllowed[];
 extern const char kEasyUnlockEnabled[];
+extern const char kEasyUnlockPairing[];
+extern const char kEasyUnlockProximityRequired[];
 extern const char kEasyUnlockShowTutorial[];
-extern const char kEasyUnlockPairing[];
-extern const char kEasyUnlockAllowed[];
 
 extern const char kZeroSuggestCachedResults[];
 
 // Local state prefs. Please add Profile prefs above instead.
 extern const char kCertRevocationCheckingEnabled[];
 extern const char kCertRevocationCheckingRequiredLocalAnchors[];
 extern const char kSSLVersionMin[];
 extern const char kSSLVersionMax[];
 extern const char kSSLVersionFallbackMin[];
 extern const char kCipherSuiteBlacklist[];
@@ skipping 383 matching lines @@
 
 extern const char kQuickCheckEnabled[];
 extern const char kBrowserGuestModeEnabled[];
 extern const char kBrowserAddPersonEnabled[];
 
 extern const char kEasyUnlockHardlockState[];
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_