Implement the Notification `timestamp` property

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

 // 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.
 
 package org.chromium.chrome.browser.notifications;
 
 import android.app.Notification;
 import android.content.Context;
 import android.content.res.Resources;
 import android.graphics.Bitmap;
@@ skipping 105 matching lines @@
             bigView.setViewVisibility(R.id.small_icon_footer, View.VISIBLE);
         }
 
         NotificationCompat.Builder builder = new NotificationCompat.Builder(mContext);
         builder.setTicker(mTickerText);
         builder.setSmallIcon(mSmallIconId);
         builder.setContentIntent(mContentIntent);
         builder.setDeleteIntent(mDeleteIntent);
         builder.setDefaults(mDefaults);
         builder.setVibrate(mVibratePattern);
+        builder.setWhen(mTimestamp);
         builder.setContent(compactView);
 
         // Some things are duplicated in the builder to ensure the notification shows correctly on
         // Wear devices and custom lock screens.
         builder.setContentTitle(mTitle);
         builder.setContentText(mBody);
         builder.setSubText(mOrigin);
         builder.setLargeIcon(mLargeIcon);
         for (Action action : mActions) {
             builder.addAction(action);
@@ skipping 134 matching lines @@
                 TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, value, displayMetrics));
     }
 
     /**
      * Whether to use the Material look and feel or fall back to Holo.
      */
     private static boolean useMaterial() {
         return Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP;
     }
 }