Make ui::InputDeviceEventObserver provide a default implementation

ui/events/devices/x11/device_data_manager_x11_unittest.cc

 // 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.
 
 #include "ui/events/devices/x11/device_data_manager_x11.h"
 
 #include <vector>
 
 // Generically-named #defines from Xlib that conflict with symbols in GTest.
 #undef Bool
@@ skipping 17 matching lines @@
     if (manager_)
       manager_->AddObserver(this);
   }
 
   ~TestInputDeviceObserver() override {
     if (manager_)
       manager_->RemoveObserver(this);
   }
 
   // InputDeviceEventObserver implementation.
-  void OnTouchscreenDeviceConfigurationChanged() override {}
   void OnKeyboardDeviceConfigurationChanged() override {
     change_notified_ = true;
   }
-  void OnMouseDeviceConfigurationChanged() override {}
-  void OnTouchpadDeviceConfigurationChanged() override {}
 
   int change_notified() const { return change_notified_; }
   void Reset() { change_notified_ = false; }
 
  private:
   DeviceDataManager* manager_;
   bool change_notified_;
 
   DISALLOW_COPY_AND_ASSIGN(TestInputDeviceObserver);
 };
@@ skipping 121 matching lines @@
   // Replug in the first device. Should be notified of the new device.
   SetKeyboardDevices(all_keyboards);
   EXPECT_TRUE(observer.change_notified());
   devices = manager->keyboard_devices();
   // Both devices now present.
   EXPECT_EQ(2u, devices.size());
 }
 
 }  // namespace test
 }  // namespace ui