[ios] Adds code to support the iOS Handoff feature.

ios/chrome/browser/device_sharing/handoff_manager.h

+// 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.
+
+#ifndef IOS_CHROME_BROWSER_DEVICE_SHARING_HANDOFF_MANAGER_H_
+#define IOS_CHROME_BROWSER_DEVICE_SHARING_HANDOFF_MANAGER_H_
+
+#include <Foundation/Foundation.h>
+
+class GURL;
+
+namespace user_prefs {
+class PrefRegistrySyncable;
+}  // namespace user_prefs
+
+// Maintains all of the state relevant to the Handoff feature. Allows Chrome to
+// hand off the current active URL to the default browser of other devices.
+@interface HandoffManager : NSObject

[erikchen, 2016/11/07 19:02:58]

isn't there already a HandoffManager?

components/handoff/handoff_manager.h

[rohitrao (ping after 24h), 2016/11/08 02:19:42]

Acknowledged.

+
+// Registers preferences related to Handoff.
++ (void)registerBrowserStatePrefs:(user_prefs::PrefRegistrySyncable*)registry;
+
+// The active URL is defined as the URL of the most recently accessed tab. This
+// method should be called any time the active URL might have changed. This
+// method is idempotent.
+- (void)updateActiveURL:(const GURL&)url;
+
+@end
+
+@interface HandoffManager (TestingOnly)
+- (NSURL*)userActivityWebpageURL;
+@end
+
+#endif  // IOS_CHROME_BROWSER_DEVICE_SHARING_HANDOFF_MANAGER_H_