Remove 'Enable tap-to-click' checkbox for non-touchpad devices.

chrome/browser/chromeos/system/touchpad_settings.h

 // Copyright (c) 2011 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 CHROME_BROWSER_CHROMEOS_SYSTEM_TOUCHPAD_SETTINGS_H_
 #define CHROME_BROWSER_CHROMEOS_SYSTEM_TOUCHPAD_SETTINGS_H_
 #pragma once
 
 namespace chromeos {
 namespace system {
 namespace touchpad_settings {
 
+bool TouchpadExists();
+
 // Sets the touchpad sensitivity in range from 1 to 5.
 void SetSensitivity(int value);
 
 // Turns tap to click on / off.
 void SetTapToClick(bool enabled);
 
 }  // namespace touchpad_settings
 }  // namespace system
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SYSTEM_TOUCHPAD_SETTINGS_H_