[Downloads] Remove externally deleted items from downloads history

chrome/android/java/src/org/chromium/chrome/browser/download/DownloadPage.java

Index: chrome/android/java/src/org/chromium/chrome/browser/download/DownloadPage.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadPage.java b/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadPage.java
index adb08deda689f02cfc5d52937959f37580520775..fd711bb7701ca2242cd0178de9fb77776d20ab98 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadPage.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/download/DownloadPage.java
@@ -7,6 +7,11 @@ package org.chromium.chrome.browser.download;
 import android.app.Activity;
 import android.view.View;
 
+import org.chromium.base.ActivityState;
+import org.chromium.base.ApplicationStatus;
+import org.chromium.base.ApplicationStatus.ActivityStateListener;
+import org.chromium.base.ThreadUtils;
+import org.chromium.base.annotations.SuppressFBWarnings;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.BasicNativePage;
 import org.chromium.chrome.browser.UrlConstants;
@@ -17,11 +22,13 @@ import org.chromium.chrome.browser.tab.Tab;
  * Native page for managing downloads handled through Chrome.
  */
 public class DownloadPage extends BasicNativePage {
+    private static ActivityStateListener sActivityStateListener;
+
     private DownloadManagerUi mManager;
     private String mTitle;
 
     /**
-     * Create a new instance of the bookmarks page.
+     * Create a new instance of the downloads page.
      * @param activity The activity to get context and manage fragments.
      * @param tab The tab to load urls.
      */
@@ -30,10 +37,28 @@ public class DownloadPage extends BasicNativePage {
     }
 
     @Override
-    protected void initialize(Activity activity, Tab tab) {
+    @SuppressFBWarnings("LI_LAZY_INIT_UPDATE_STATIC")  // Not called from multiple threads.
+    protected void initialize(Activity activity, final Tab tab) {
+        ThreadUtils.assertOnUiThread();
+
         mManager = new DownloadManagerUi(activity, tab.isIncognito(), activity.getComponentName());
         mManager.setBasicNativePage(this);
         mTitle = activity.getString(R.string.download_manager_ui_all_downloads);
+
+        // Only register one activity state listener to prevent issuing multiple calls to check for
+        // externally removed downloads if multiple tabs are showing the downloads page.
+        if (sActivityStateListener == null) {
+            sActivityStateListener = new ActivityStateListener() {
+                @Override
+                public void onActivityStateChange(Activity activity, int newState) {
+                    if (newState == ActivityState.RESUMED) {
+                        DownloadUtils.checkForExternallyRemovedDownloads(
+                                activity.getApplicationContext(), tab.isIncognito());
+                    }
+                }
+            };
+            ApplicationStatus.registerStateListenerForActivity(sActivityStateListener, activity);
+        }
     }
 
     @Override