Implement the Notification `timestamp` property

chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationUIManager.java

Index: chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationUIManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationUIManager.java b/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationUIManager.java
index 965a3871c195be90ca9e3e9ca1d00160dd1f0d5a..8a466f93519be9896ada5900d1982be60e1a9586 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationUIManager.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationUIManager.java
@@ -397,14 +397,15 @@ public class NotificationUIManager {
      * @param icon Icon to be displayed in the notification. Valid Bitmap icons will be scaled to
      *             the platforms, whereas a default icon will be generated for invalid Bitmaps.
      * @param vibrationPattern Vibration pattern following the Web Vibration syntax.
+     * @param timestamp The timestamp of the event for which the notification is being shown.
      * @param silent Whether the default sound, vibration and lights should be suppressed.
      * @param actionTitles Titles of actions to display alongside the notification.
      * @see https://developer.android.com/reference/android/app/Notification.html
      */
     @CalledByNative
     private void displayNotification(long persistentNotificationId, String origin, String tag,
-            String title, String body, Bitmap icon, int[] vibrationPattern, boolean silent,
-            String[] actionTitles) {
+            String title, String body, Bitmap icon, int[] vibrationPattern, long timestamp,
+            boolean silent, String[] actionTitles) {
         Resources res = mAppContext.getResources();
 
         // Set up a pending intent for going to the settings screen for |origin|.
@@ -431,6 +432,7 @@ public class NotificationUIManager {
                         NotificationConstants.ACTION_CLOSE_NOTIFICATION,
                         persistentNotificationId, origin, tag, -1 /* actionIndex */))
                 .setTicker(createTickerText(title, body))
+                .setWhen(timestamp)
                 .setSubText(origin);
 
         for (int actionIndex = 0; actionIndex < actionTitles.length; actionIndex++) {