Enable lost URL detection in the Physical Web scanner

ios/chrome/common/physical_web/physical_web_device.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.
 
 #import "ios/chrome/common/physical_web/physical_web_device.h"
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
 #include "ios/chrome/common/physical_web/physical_web_types.h"
 
 @implementation PhysicalWebDevice {
   base::scoped_nsobject<NSURL> url_;
   base::scoped_nsobject<NSURL> requestURL_;
   base::scoped_nsobject<NSURL> icon_;
   base::scoped_nsobject<NSString> title_;
   base::scoped_nsobject<NSString> description_;
   int rssi_;
   int transmitPower_;
   double rank_;
+  base::scoped_nsobject<NSDate> scanTimestamp_;
 }
 
 @synthesize rssi = rssi_;
 @synthesize transmitPower = transmitPower_;
 @synthesize rank = rank_;
 
 - (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 {
+                       rank:(double)rank
+              scanTimestamp:(NSDate*)scanTimestamp {
   self = [super init];
   if (self) {
     url_.reset([url retain]);
     requestURL_.reset([requestURL retain]);
     icon_.reset([icon retain]);
     title_.reset([title copy]);
     description_.reset([description copy]);
     transmitPower_ = transmitPower;
     rssi_ = rssi;
     rank_ = rank > physical_web::kMaxRank ? physical_web::kMaxRank : rank;
+    scanTimestamp_.reset([scanTimestamp retain]);
   }
   return self;
 }
 
 - (instancetype)init {
   NOTREACHED();
   return nil;
 }
 
 - (NSURL*)url {
   return url_;
 }
 
 - (NSURL*)requestURL {
   return requestURL_;
 }
 
 - (NSURL*)icon {
   return icon_;
 }
 
 - (NSString*)title {
   return title_;
 }
 
 - (NSString*)description {
   return description_;
 }
 
+- (NSDate*)scanTimestamp {
+  return scanTimestamp_;
+}
+
+- (void)setScanTimestamp:(NSDate*)value {
+  scanTimestamp_.reset([value retain]);
+}
+
 @end