Enable lost URL detection in the Physical Web scanner

ios/chrome/common/physical_web/physical_web_device.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_COMMON_PHYSICAL_WEB_PHYSICAL_WEB_DEVICE_H_
 #define IOS_CHROME_COMMON_PHYSICAL_WEB_PHYSICAL_WEB_DEVICE_H_
 
 #import <Foundation/Foundation.h>
 
 @interface PhysicalWebDevice : NSObject
 
 // Initializes a physical web device. See below for the description of the
 // properties.
 - (instancetype)initWithURL:(NSURL*)url
                  requestURL:(NSURL*)requestURL
                        icon:(NSURL*)icon
                       title:(NSString*)title
                 description:(NSString*)description
               transmitPower:(int)transmitPower
                        rssi:(int)rssi
-                       rank:(double)rank NS_DESIGNATED_INITIALIZER;
+                       rank:(double)rank
+              scanTimestamp:(NSDate*)scanTimestamp NS_DESIGNATED_INITIALIZER;
 
 - (instancetype)init NS_UNAVAILABLE;
 
 // |url| is the expanded URL.
 @property(nonatomic, readonly, retain) NSURL* url;
 
 // |requestUrl| is the broadcast URL.
 @property(nonatomic, readonly, retain) NSURL* requestURL;
 
 // |icon| is the URL of the favicon.
 @property(nonatomic, readonly, retain) NSURL* icon;
 
 // |title| is the title of the webpage.
 @property(nonatomic, readonly, retain) NSString* title;
 
 // |description| is a short text description of the webpage content.
 @property(nonatomic, readonly, retain) NSString* description;
 
 // |transmitPower| is the UriBeacon Tx Power Level.
 @property(nonatomic, readonly) int transmitPower;
 
 // |rssi| is the received signal strength indicator (RSSI) of the peripheral, in
 // decibels.
 @property(nonatomic, readonly) int rssi;
 
 // |rank| of the physical web device returned by the server.
 @property(nonatomic, readonly) double rank;
 
+// |scanTimestamp| is the time the URL was most recently seen.
+@property(nonatomic, retain) NSDate* scanTimestamp;
+
 @end
 
 #endif  // IOS_CHROME_COMMON_PHYSICAL_WEB_PHYSICAL_WEB_DEVICE_H_