Enable a ripple on the roots list in DocumentsUI.

Change-Id: I380cd66ace4ee1478e5a182545f916ac39e47d8d
diff --git a/packages/DocumentsUI/res/drawable/item_root_background.xml b/packages/DocumentsUI/res/drawable/item_root_background.xml
index 93c965f..c403159 100644
--- a/packages/DocumentsUI/res/drawable/item_root_background.xml
+++ b/packages/DocumentsUI/res/drawable/item_root_background.xml
@@ -21,5 +21,4 @@
     <item android:state_focused="false" android:state_activated="true">
         <color android:color="@color/material_grey_300" />
     </item>
-    <item android:drawable="@android:color/transparent" />
 </selector>
diff --git a/packages/DocumentsUI/res/layout/fragment_roots.xml b/packages/DocumentsUI/res/layout/fragment_roots.xml
index 2d624d8..f3de3b4 100644
--- a/packages/DocumentsUI/res/layout/fragment_roots.xml
+++ b/packages/DocumentsUI/res/layout/fragment_roots.xml
@@ -19,4 +19,5 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:paddingTop="8dp"
+    android:drawSelectorOnTop="true"
     android:divider="@null" />