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/VirtualTouchpadService.h b/services/vr/virtual_touchpad/VirtualTouchpadService.h
index b832c8f..9b880b2 100644
--- a/services/vr/virtual_touchpad/VirtualTouchpadService.h
+++ b/services/vr/virtual_touchpad/VirtualTouchpadService.h
@@ -15,11 +15,12 @@
  public:
   VirtualTouchpadService(sp<VirtualTouchpad> touchpad)
       : touchpad_(touchpad) {}
+  ~VirtualTouchpadService() override {}
 
  protected:
   // Implements IVirtualTouchpadService.
-  binder::Status touch(float x, float y, float pressure) override;
-  binder::Status buttonState(int buttons) override;
+  binder::Status touch(int touchpad, float x, float y, float pressure) override;
+  binder::Status buttonState(int touchpad, int buttons) override;
 
  private:
   sp<VirtualTouchpad> touchpad_;