Implement GetDisplayed on android M+

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

Index: chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationManagerProxyImpl.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationManagerProxyImpl.java b/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationManagerProxyImpl.java
index b05fd0047b17adb015a4506b96e789b5e158fdd9..ece1f75cde2ef1586e854068ef684709f1bb9da9 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationManagerProxyImpl.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationManagerProxyImpl.java
@@ -6,6 +6,7 @@ package org.chromium.chrome.browser.notifications;
 
 import android.app.Notification;
 import android.app.NotificationManager;
+import android.service.notification.StatusBarNotification;
 
 /**
  * Default implementation of the NotificationManagerProxy, which passes through all calls to the
@@ -42,4 +43,9 @@ public class NotificationManagerProxyImpl implements NotificationManagerProxy {
     public void notify(String tag, int id, Notification notification) {
         mNotificationManager.notify(tag, id, notification);
     }
+
+    @Override
+    public StatusBarNotification[] getActiveNotifications() {
+        return mNotificationManager.getActiveNotifications();
+    }
 }