Remove --ash-enable-tray-dragging flag

ash/ash.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
     'grit_out_dir': '<(SHARED_INTERMEDIATE_DIR)/chrome',
     # These files lists are shared with the GN build.
     'ash_sources': [
@@ skipping 490 matching lines @@
       'wm/drag_window_resizer.cc',
       'wm/drag_window_resizer.h',
       'wm/event_client_impl.cc',
       'wm/event_client_impl.h',
       'wm/gestures/long_press_affordance_handler.cc',
       'wm/gestures/long_press_affordance_handler.h',
       'wm/gestures/overview_gesture_handler.cc',
       'wm/gestures/overview_gesture_handler.h',
       'wm/gestures/shelf_gesture_handler.cc',
       'wm/gestures/shelf_gesture_handler.h',
-      'wm/gestures/tray_gesture_handler.cc',
-      'wm/gestures/tray_gesture_handler.h',
       'wm/immersive_fullscreen_controller.cc',
       'wm/immersive_fullscreen_controller.h',
       'wm/immersive_revealed_lock.cc',
       'wm/immersive_revealed_lock.h',
       'wm/lock_layout_manager.cc',
       'wm/lock_layout_manager.h',
       'wm/lock_state_controller.cc',
       'wm/lock_state_controller.h',
       'wm/lock_state_observer.h',
       'wm/lock_window_state.cc',
@@ skipping 764 matching lines @@
             '../build/isolate.gypi',
           ],
           'sources': [
             'ash_unittests.isolate',
           ],
         },
       ],
     }],
   ],
 }