Add flag to enable immersive fullscreen for v2 apps

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 406 matching lines @@
         'wm/base_layout_manager.cc',
         'wm/base_layout_manager.h',
         'wm/boot_splash_screen_chromeos.cc',
         'wm/boot_splash_screen_chromeos.h',
         'wm/caption_buttons/alternate_frame_caption_button.cc',
         'wm/caption_buttons/alternate_frame_caption_button.h',
         'wm/caption_buttons/frame_caption_button_container_view.cc',
         'wm/caption_buttons/frame_caption_button_container_view.h',
         'wm/caption_buttons/frame_maximize_button.cc',
         'wm/caption_buttons/frame_maximize_button.h',
+        'wm/caption_buttons/frame_maximize_button_observer.h',
         'wm/caption_buttons/maximize_bubble_controller.cc',
         'wm/caption_buttons/maximize_bubble_controller.h',
         'wm/caption_buttons/maximize_bubble_frame_state.h',
         'wm/coordinate_conversion.cc',
         'wm/coordinate_conversion.h',
         'wm/custom_frame_view_ash.cc',
         'wm/custom_frame_view_ash.h',
         'wm/default_window_resizer.cc',
         'wm/default_window_resizer.h',
         'wm/dock/docked_window_layout_manager.cc',
@@ skipping 527 matching lines @@
             },
           },
           'dependencies': [
             '../sandbox/sandbox.gyp:sandbox',
           ],
         }],
       ],
     },
   ],
 }