Interface for multiple virtual touchpads.

This passes the touchpad selection across binder, but does not yet
actually implement multiple touchpad devices.

Bug: b/35992608
Test: primary only in VirtualTouchpad_test
Change-Id: I7529735362e0e38805b9c0e52e07b5efc86bd535
diff --git a/services/vr/virtual_touchpad/VirtualTouchpadEvdev.h b/services/vr/virtual_touchpad/VirtualTouchpadEvdev.h
index c763529..ec8006b 100644
--- a/services/vr/virtual_touchpad/VirtualTouchpadEvdev.h
+++ b/services/vr/virtual_touchpad/VirtualTouchpadEvdev.h
@@ -18,12 +18,12 @@
   static sp<VirtualTouchpad> Create();
 
   // VirtualTouchpad implementation:
-  status_t Touch(float x, float y, float pressure) override;
-  status_t ButtonState(int buttons) override;
+  status_t Touch(int touchpad, float x, float y, float pressure) override;
+  status_t ButtonState(int touchpad, int buttons) override;
 
  protected:
   VirtualTouchpadEvdev() {}
-  ~VirtualTouchpadEvdev() {}
+  ~VirtualTouchpadEvdev() override {}
   status_t Initialize();
 
   // Must be called only between construction and Initialize().