ozone: Map TouchEvent::touch_id_ into expected range

ui/events/ozone/evdev/event_converter_evdev.h

Index: ui/events/ozone/evdev/event_converter_evdev.h
diff --git a/ui/events/ozone/evdev/event_converter_evdev.h b/ui/events/ozone/evdev/event_converter_evdev.h
index eaa4059274ae60fbf34d93685bc559fb9003d7aa..eca7702ec3d57c5b4b56cecb1503fee79b7ec6b9 100644
--- a/ui/events/ozone/evdev/event_converter_evdev.h
+++ b/ui/events/ozone/evdev/event_converter_evdev.h
@@ -69,6 +69,10 @@ class EVENTS_OZONE_EVDEV_EXPORT EventConverterEvdev
   // called unless HasTouchscreen() returns true
   virtual int GetTouchPoints() const;
 
+  // Offset to apply to the touch_id on events generated in order to give
+  // globally unique identifiers.
+  virtual void SetTouchIdOffset(int offset);
+
   // Sets which keyboard keys should be processed.
   virtual void SetAllowedKeys(scoped_ptr<std::set<DomCode>> allowed_keys);