Added a command line switch to disable xinput2, enabled xinput2 by default

ui/events/devices/x11/device_data_manager_x11.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_DEVICES_X11_DEVICE_DATA_MANAGER_X11_H_
 #define UI_EVENTS_DEVICES_X11_DEVICE_DATA_MANAGER_X11_H_
 
 // Generically-named #defines from Xlib is conflicting with symbols in GTest.
 // So many tests .cc file #undef Bool before including device_data_manager.h,
 // which makes Bool unrecognized in XInput2.h.
@@ skipping 341 matching lines @@
   // The set of keys allowed while the keyboard is blocked.
   std::unique_ptr<std::set<KeyboardCode>> blocked_keyboard_allowed_keys_;
 
   // Number of valuators on the specific device.
   int valuator_count_[kMaxDeviceNum];
 
   // Index table to find the valuator for DataType on the specific device
   // by valuator_lookup_[device_id][data_type].
   std::vector<int> valuator_lookup_[kMaxDeviceNum];
 
+  // Indicates if the user has disabled high precision scrolling support.
+  bool high_precision_scrolling_disabled_;
+
   // Index table to find the horizontal and vertical scroll valuator
   // numbers, scroll increments and scroll position.
   ScrollInfo scroll_data_[kMaxDeviceNum];
 
   // Index table to find the DataType for valuator on the specific device
   // by data_type_lookup_[device_id][valuator].
   std::vector<int> data_type_lookup_[kMaxDeviceNum];
 
   // Index table to find the min & max value of the Valuator on a specific
   // device.
@@ skipping 18 matching lines @@
 
   unsigned char button_map_[256];
   int button_map_count_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceDataManagerX11);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_DEVICES_X11_DEVICE_DATA_MANAGER_X11_H_