Show the downloads list divided into groups based on how recently downloaded.

Fixes http://b/issue?id=2367226
diff --git a/res/layout/browser_downloads_page.xml b/res/layout/browser_downloads_page.xml
index 1d4d4e6..06c27c6 100644
--- a/res/layout/browser_downloads_page.xml
+++ b/res/layout/browser_downloads_page.xml
@@ -19,8 +19,8 @@
 */
 -->
 <merge xmlns:android="http://schemas.android.com/apk/res/android">
-    <ListView 
-        android:id="@+id/list"
+    <ExpandableListView
+        android:id="@android:id/list"
         android:layout_width="fill_parent"
         android:layout_height="fill_parent"/>
     <ViewStub