Auto-detect whether to use the long-press UI.

Change-Id: Ie77a5584e301467c6a5e164d2c62d6f036b2c0c0
diff --git a/device.h b/device.h
index 3d9101b..1507183 100644
--- a/device.h
+++ b/device.h
@@ -54,7 +54,7 @@
     //   - invoke the highlighted item (kInvokeItem)
     //   - do nothing (kNoAction)
     //   - invoke a specific action (a menu position: any non-negative number)
-    virtual int HandleMenuKey(int key, int visible) = 0;
+    virtual int HandleMenuKey(int key, int visible);
 
     enum BuiltinAction {
         NO_ACTION = 0,