First pass of the Launcher Overlay interface / impl

-> Added simple reference launcher extension
-> Make launcher able to handle a null qsb

Change-Id: Ib1575243cac800a335e95bbf00cdc394bb4741c3
diff --git a/res/layout-sw720dp/launcher.xml b/res/layout-sw720dp/launcher.xml
index 6261541..87fa2ed 100644
--- a/res/layout-sw720dp/launcher.xml
+++ b/res/layout-sw720dp/launcher.xml
@@ -82,4 +82,12 @@
             android:layout_height="match_parent"
             android:visibility="invisible" />
     </com.android.launcher3.DragLayer>
+
+    <ViewStub
+        android:id="@+id/launcher_overlay_stub"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:inflatedId="@+id/launcher_overlay"
+        android:layout="@layout/launcher_overlay" />
+
 </FrameLayout>