ozone: Map TouchEvent::touch_id_ into expected range

ui/events/ozone/evdev/touch_event_converter_evdev.h

Index: ui/events/ozone/evdev/touch_event_converter_evdev.h
diff --git a/ui/events/ozone/evdev/touch_event_converter_evdev.h b/ui/events/ozone/evdev/touch_event_converter_evdev.h
index c1b78946a4fe5dfb7fb8ee5cf24c359a9b39f246..b4e2ab43cb9cdb75c05e2fd61af7245dfa8be193 100644
--- a/ui/events/ozone/evdev/touch_event_converter_evdev.h
+++ b/ui/events/ozone/evdev/touch_event_converter_evdev.h
@@ -37,6 +37,7 @@ class EVENTS_OZONE_EVDEV_EXPORT TouchEventConverterEvdev
   bool HasTouchscreen() const override;
   gfx::Size GetTouchscreenSize() const override;
   int GetTouchPoints() const override;
+  void SetTouchIdOffset(int offset) override;
 
   // Unsafe part of initialization.
   virtual void Initialize(const EventDeviceInfo& info);
@@ -99,6 +100,9 @@ class EVENTS_OZONE_EVDEV_EXPORT TouchEventConverterEvdev
   // Touch point currently being updated from the /dev/input/event* stream.
   size_t current_slot_;
 
+  // Offset to apply for this touch device to give unique event touch_ids.
+  int touch_id_offset_;
+
   // In-progress touch points.
   std::vector<InProgressTouchEvdev> events_;