[Offline Pages] Fixing prefetched pages shown in notification.

Prefetched pages were shown occasionally since an OnItemUpdate would be
invoked if thumbnail of the page downloaded was fetched.

Issue is fixed by adding early returns in OCANBUi.onItemUpdated, same
check is added for onItemAdded as well.

Bug: 852054
Change-Id: Iccdbf1dda0ebe39a10de954848304988118ba90d
Reviewed-on: https://chromium-review.googlesource.com/1103549
Commit-Queue: Yafei Duan <romax@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Reviewed-by: Dmitry Titov <dimich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569360}

chrome/android/java/src/org/chromium/chrome/browser/download/items/OfflineContentAggregatorNotificationBridgeUi.java

@@ -9,6 +9,7 @@ import org.chromium.chrome.browser.download.DownloadItem;
 import org.chromium.chrome.browser.download.DownloadNotifier;
 import org.chromium.chrome.browser.download.DownloadServiceDelegate;
 import org.chromium.components.offline_items_collection.ContentId;
+import org.chromium.components.offline_items_collection.LegacyHelpers;
 import org.chromium.components.offline_items_collection.OfflineContentProvider;
 import org.chromium.components.offline_items_collection.OfflineItem;
 import org.chromium.components.offline_items_collection.OfflineItemState;
@@ -86,7 +87,6 @@ public class OfflineContentAggregatorNotificationBridgeUi
 
     @Override
     public void onItemUpdated(OfflineItem item) {
-        // Assume that any item sending updates should have them reflected in the UI.
         getVisualsAndUpdateItem(item);
     }
 
@@ -147,6 +147,10 @@ public class OfflineContentAggregatorNotificationBridgeUi
     }
 
     private void pushItemToUi(OfflineItem item, OfflineItemVisuals visuals) {
+        // TODO(http://crbug.com/855141): Find a cleaner way to hide unimportant UI updates.
+        // If it's a suggested page, do not add it to the notification UI.
+        if (LegacyHelpers.isLegacyOfflinePage(item.id) && item.isSuggested) return;
+
         DownloadInfo info = DownloadInfo.fromOfflineItem(item, visuals);
         switch (item.state) {
             case OfflineItemState.IN_PROGRESS: