now able to set the layer stack on a DisplayDevice

Change-Id: Ia9691cf221b9444c243eb468d9e276a30e600b6b
diff --git a/services/surfaceflinger/DisplayDevice.h b/services/surfaceflinger/DisplayDevice.h
index 78d44f3..7efd3bc 100644
--- a/services/surfaceflinger/DisplayDevice.h
+++ b/services/surfaceflinger/DisplayDevice.h
@@ -91,6 +91,8 @@
     bool                    getSecureLayerVisible() const;
 
     status_t                setOrientation(int orientation);
+    void                    setLayerStack(uint32_t stack);
+
     int                     getOrientation() const { return mOrientation; }
     const Transform&        getTransform() const { return mGlobalTransform; }
     uint32_t                getLayerStack() const { return mLayerStack; }