Use WindowTracker when resizing root window as it may delete other window in unit tests.

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,
     # These files lists are shared with the GN build.
     'ash_sources': [
       'accelerators/accelerator_commands.cc',
@@ skipping 890 matching lines @@
       'wm/lock_state_controller_unittest.cc',
       'wm/maximize_mode/accelerometer_test_data_literals.cc',
       'wm/maximize_mode/maximize_mode_controller_unittest.cc',
       'wm/maximize_mode/maximize_mode_window_manager_unittest.cc',
       'wm/mru_window_tracker_unittest.cc',
       'wm/overlay_event_filter_unittest.cc',
       'wm/overview/window_selector_unittest.cc',
       'wm/panels/panel_layout_manager_unittest.cc',
       'wm/panels/panel_window_resizer_unittest.cc',
       'wm/resize_shadow_and_cursor_unittest.cc',
+      'wm/root_window_layout_manager_unittest.cc',
       'wm/screen_dimmer_unittest.cc',
       'wm/session_state_animator_impl_unittest.cc',
       'wm/stacking_controller_unittest.cc',
       'wm/system_gesture_event_filter_unittest.cc',
       'wm/system_modal_container_layout_manager_unittest.cc',
       'wm/toplevel_window_event_handler_unittest.cc',
       'wm/video_detector_unittest.cc',
       'wm/window_animations_unittest.cc',
       'wm/window_cycle_controller_unittest.cc',
       'wm/window_manager_unittest.cc',
@@ skipping 443 matching lines @@
                   '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
                 ],
               }
             ],
           ],
         },
       ],
     }],
   ],
 }