ozone: Map TouchEvent::touch_id_ into expected range

ui/events/ozone/evdev/touch_event_converter_evdev.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_EVENTS_OZONE_EVDEV_TOUCH_EVENT_CONVERTER_EVDEV_H_
 #define UI_EVENTS_OZONE_EVDEV_TOUCH_EVENT_CONVERTER_EVDEV_H_
 
 #include <bitset>
 
 #include "base/compiler_specific.h"
@@ skipping 19 matching lines @@
                            base::FilePath path,
                            int id,
                            InputDeviceType type,
                            DeviceEventDispatcherEvdev* dispatcher);
   ~TouchEventConverterEvdev() override;
 
   // EventConverterEvdev:
   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);
 
  private:
   friend class MockTouchEventConverterEvdev;
 
   // Overidden from base::MessagePumpLibevent::Watcher.
   void OnFileCanReadWithoutBlocking(int fd) override;
 
@@ skipping 42 matching lines @@
 
   // Number of touch points reported by driver
   int touch_points_;
 
   // Tracking id counter.
   int next_tracking_id_;
 
   // 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_;
 
   // Finds touch noise.
   scoped_ptr<TouchNoiseFinder> touch_noise_finder_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchEventConverterEvdev);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_OZONE_EVDEV_TOUCH_EVENT_CONVERTER_EVDEV_H_