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

Change-Id: Ie77a5584e301467c6a5e164d2c62d6f036b2c0c0
diff --git a/ui.h b/ui.h
index 0d5ab55..c5c65c2 100644
--- a/ui.h
+++ b/ui.h
@@ -75,6 +75,10 @@
     virtual bool IsKeyPressed(int key);
     virtual bool IsLongPress();
 
+    // Returns true if you have the volume up/down and power trio typical
+    // of phones and tablets, false otherwise.
+    virtual bool HasThreeButtons();
+
     // Erase any queued-up keys.
     virtual void FlushKeys();