Split //ios/chrome/browser/prefs to prevent circular dependencies.

ios/chrome/browser/device_sharing/device_sharing_manager.mm

 // Copyright 2015 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 "ios/chrome/browser/device_sharing/device_sharing_manager.h"
 
 #include <memory>
 
 #include "base/mac/scoped_nsobject.h"
 #import "components/handoff/handoff_manager.h"
+#include "components/handoff/pref_names_ios.h"
 #include "components/prefs/pref_change_registrar.h"
 #include "components/prefs/pref_service.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
-#include "ios/chrome/browser/pref_names.h"
 #include "ios/chrome/browser/prefs/pref_observer_bridge.h"
 #include "url/gurl.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 @interface DeviceSharingManager ()<PrefObserverDelegate> {
   ios::ChromeBrowserState* _browserState;  // weak
 
@@ skipping 73 matching lines @@
 
 @end
 
 @implementation DeviceSharingManager (TestingOnly)
 
 - (HandoffManager*)handoffManager {
   return _handoffManager.get();
 }
 
 @end