Enable lost URL detection in the Physical Web scanner

ios/chrome/common/physical_web/physical_web_device.h

Index: ios/chrome/common/physical_web/physical_web_device.h
diff --git a/ios/chrome/common/physical_web/physical_web_device.h b/ios/chrome/common/physical_web/physical_web_device.h
index b54d5de16f960c5f4464c8411e4327268413aff3..9bbcba852b17adb7f717c4b64e3bde06ce8442bc 100644
--- a/ios/chrome/common/physical_web/physical_web_device.h
+++ b/ios/chrome/common/physical_web/physical_web_device.h
@@ -18,7 +18,8 @@
                 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;
 
@@ -47,6 +48,9 @@
 // |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_