Fix Volume slider is captured in screenshot done in touchview mode

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_aura.cc',
@@ skipping 360 matching lines @@
       'common/wm/focus_rules.h',
       'common/wm/forwarding_layer_delegate.cc',
       'common/wm/forwarding_layer_delegate.h',
       'common/wm/fullscreen_window_finder.cc',
       'common/wm/fullscreen_window_finder.h',
       'common/wm/lock_state_observer.h',
       'common/wm/maximize_mode/maximize_mode_controller.cc',
       'common/wm/maximize_mode/maximize_mode_controller.h',
       'common/wm/maximize_mode/maximize_mode_event_handler.cc',
       'common/wm/maximize_mode/maximize_mode_event_handler.h',
+      'common/wm/maximize_mode/maximize_mode_screenshot_observer.h',
       'common/wm/maximize_mode/maximize_mode_window_manager.cc',
       'common/wm/maximize_mode/maximize_mode_window_manager.h',
       'common/wm/maximize_mode/maximize_mode_window_state.cc',
       'common/wm/maximize_mode/maximize_mode_window_state.h',
       'common/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard.h',
       'common/wm/maximize_mode/workspace_backdrop_delegate.cc',
       'common/wm/maximize_mode/workspace_backdrop_delegate.h',
       'common/wm/mru_window_tracker.cc',
       'common/wm/mru_window_tracker.h',
       'common/wm/overview/cleanup_animation_observer.cc',
@@ skipping 1080 matching lines @@
                   '../tools/xdisplaycheck/xdisplaycheck.gyp:xdisplaycheck',
                 ],
               }
             ],
           ],
         },
       ],
     }],
   ],
 }