Adding a gray semi transparent backdrop behind the topmost window within the default container

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',
   },
   'includes': [
@@ skipping 518 matching lines @@
         'wm/image_cursors.h',
         'wm/immersive_fullscreen_controller.cc',
         'wm/immersive_fullscreen_controller.h',
         'wm/immersive_revealed_lock.cc',
         'wm/immersive_revealed_lock.h',
         'wm/lock_state_controller.cc',
         'wm/lock_state_controller.h',
         'wm/lock_state_observer.h',
         'wm/maximize_mode/maximize_mode_window_manager.cc',
         'wm/maximize_mode/maximize_mode_window_manager.h',        
+        'wm/maximize_mode/workspace_backdrop_delegate.cc',
+        'wm/maximize_mode/workspace_backdrop_delegate.h',
         'wm/mru_window_tracker.cc',
         'wm/mru_window_tracker.h',
         'wm/overlay_event_filter.cc',
         'wm/overlay_event_filter.h',
         'wm/overview/scoped_transform_overview_window.cc',
         'wm/overview/scoped_transform_overview_window.h',
         'wm/overview/scoped_window_copy.cc',
         'wm/overview/scoped_window_copy.h',
         'wm/overview/window_overview.cc',
         'wm/overview/window_overview.h',
@@ skipping 409 matching lines @@
         'wm/toplevel_window_event_handler_unittest.cc',
         'wm/user_activity_detector_unittest.cc',
         'wm/video_detector_unittest.cc',
         'wm/window_animations_unittest.cc',
         'wm/window_cycle_controller_unittest.cc',
         'wm/window_manager_unittest.cc',
         'wm/window_modality_controller_unittest.cc',
         'wm/window_positioner_unittest.cc',
         'wm/window_state_unittest.cc',
         'wm/window_util_unittest.cc',
+        'wm/maximize_mode/workspace_backdrop_delegate.cc',
+        'wm/maximize_mode/workspace_backdrop_delegate.h',
         'wm/workspace/magnetism_matcher_unittest.cc',
         'wm/workspace/multi_window_resize_controller_unittest.cc',
         'wm/workspace/phantom_window_controller_unittest.cc',
         'wm/workspace/workspace_event_handler_test_helper.cc',
         'wm/workspace/workspace_event_handler_test_helper.h',
         'wm/workspace/workspace_event_handler_unittest.cc',
         'wm/workspace/workspace_layout_manager_unittest.cc',
         'wm/workspace/workspace_window_resizer_unittest.cc',
         'wm/workspace_controller_test_helper.cc',
         'wm/workspace_controller_test_helper.h',
@@ skipping 140 matching lines @@
         }],
         ['chromeos==1', {
           'dependencies': [
             '../device/bluetooth/bluetooth.gyp:device_bluetooth',
           ],
         }],
       ],
     },
   ],
 }