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

ios/chrome/browser/device_sharing/device_sharing_manager.h

+// 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.
+
+#ifndef IOS_CHROME_BROWSER_DEVICE_SHARING_DEVICE_SHARING_MANAGER_H_
+#define IOS_CHROME_BROWSER_DEVICE_SHARING_DEVICE_SHARING_MANAGER_H_
+
+#import <Foundation/Foundation.h>
+
+class GURL;
+@class HandoffManager;
+
+namespace ios {
+class ChromeBrowserState;
+}
+
+// This manager maintains all state related to sharing the active URL to other
+// devices. It has the role of a dispatcher that shares the active URL to
+// various internal sharing services (e.g. handoff).
+@interface DeviceSharingManager : NSObject
+
+// Updates the internal browser state to |browserState|.
+// If the browser state is already |browserState|, then this is a no-op.
+// Otherwise, this method cleans up the active URL and updates the internal
+// state to reflect the new browser state.
+//
+// Note that this method keep a weak reference to |browserState|. It
+// expects its owner to clear the browser state via a call to
+// |-updateBrowserState:NULL| before |browserState| is destroyed.

[erikchen, 2016/11/07 22:02:08]

s/NULL/nullptr

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

Done.

+//
+// |browserState| must not be off the record.
+- (void)updateBrowserState:(ios::ChromeBrowserState*)browserState;
+
+// Updates the active URL to be shared with other devices. This method is
+// a no-op if the active browser state was never set previously.
+- (void)updateActiveURL:(const GURL&)activeURL;
+
+@end
+
+@interface DeviceSharingManager (TestingOnly)
+
+// Exposing Handoff feature for testing.
+@property(nonatomic, readonly) HandoffManager* handoffManager;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_DEVICE_SHARING_DEVICE_SHARING_MANAGER_H_