[Android] Implement back key functionality in download manager

chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java

Index: chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
index 7527007781ac621de15eda03326569125214ebe6..18298010c23f5f939816a8802e8e9eb06364f170 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadManagerUi.java
@@ -279,6 +279,21 @@ public class DownloadManagerUi implements OnMenuItemClickListener {
     }
 
     /**
+     * Adds a {@link DownloadUiObserver} to observe the changes in the download manager.
+     */
+    public void addObserver(DownloadUiObserver observer) {
+        mObservers.addObserver(observer);
+    }
+
+    /**
+     * Removes a {@link DownloadUiObserver} that were added in
+     * {@link #addObserver(DownloadUiObserver)}
+     */
+    public void removeObserver(DownloadUiObserver observer) {
+        mObservers.removeObserver(observer);
+    }
+
+    /**
      * @see DrawerLayout#closeDrawer(int)
      */
     void closeDrawer() {
@@ -317,21 +332,6 @@ public class DownloadManagerUi implements OnMenuItemClickListener {
                 DownloadFilter.FILTER_BOUNDARY);
     }
 
-    /**
-     * Adds a {@link DownloadUiObserver} to observe the changes in the download manager.
-     */
-    void addObserver(DownloadUiObserver observer) {
-        mObservers.addObserver(observer);
-    }
-
-    /**
-     * Removes a {@link DownloadUiObserver} that were added in
-     * {@link #addObserver(DownloadUiObserver)}
-     */
-    void removeObserver(DownloadUiObserver observer) {
-        mObservers.removeObserver(observer);
-    }
-
     private void shareSelectedItems() {
         List<DownloadHistoryItemWrapper> selectedItems =
                 mBackendProvider.getSelectionDelegate().getSelectedItems();