Implement the Notification `timestamp` property

chrome/android/javatests/src/org/chromium/chrome/browser/notifications/NotificationUIManagerTest.java

Index: chrome/android/javatests/src/org/chromium/chrome/browser/notifications/NotificationUIManagerTest.java
diff --git a/chrome/android/javatests/src/org/chromium/chrome/browser/notifications/NotificationUIManagerTest.java b/chrome/android/javatests/src/org/chromium/chrome/browser/notifications/NotificationUIManagerTest.java
index 792375e2bb46237b5a64c3c747622fcbe32c5ced..7d67124b61524ec0d61c3cd90b4c79021891ef67 100644
--- a/chrome/android/javatests/src/org/chromium/chrome/browser/notifications/NotificationUIManagerTest.java
+++ b/chrome/android/javatests/src/org/chromium/chrome/browser/notifications/NotificationUIManagerTest.java
@@ -165,6 +165,11 @@ public class NotificationUIManagerTest extends ChromeActivityTestCaseBase<Chrome
         assertTrue(tickerText.contains("MyNotification"));
         assertTrue(tickerText.contains("Hello"));
 
+        // Verify that the notification's timestamp is set in the past 30 seconds. This number has
+        // no significance, but needs to be high enough to not cause flakiness as it's set by the
+        // renderer process on notification creation.
+        assertTrue((System.currentTimeMillis() - notification.when) < 30 * 1000);

[johnme, 2015/10/20 17:12:20]

Is it worth throwing in a Math.abs just in case the renderer's clock is running
fast (e.g. if the machine synced to a NTP server in between)?

[Peter Beverloo, 2016/01/28 17:18:29]

Done.

+
         // Validate the appearance style of the notification. The EXTRA_TEMPLATE was inroduced
         // in Android Lollipop, we cannot verify this in earlier versions.
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {