exo: Add support for subcompositor interface.

components/exo.gypi

 # Copyright 2015 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.
 
 {
   'targets': [
     {
       # GN version: //components/exo
       'target_name': 'exo',
       'type': 'static_library',
@@ skipping 16 matching lines @@
       'sources': [
         # Note: sources list duplicated in GN build.
         'exo/buffer.cc',
         'exo/buffer.h',
         'exo/display.cc',
         'exo/display.h',
         'exo/shared_memory.cc',
         'exo/shared_memory.h',
         'exo/shell_surface.cc',
         'exo/shell_surface.h',
+        'exo/sub_surface.cc',
+        'exo/sub_surface.h',
         'exo/surface.cc',
         'exo/surface.h',
         'exo/surface_delegate.h',
+        'exo/surface_observer.h',
       ],
     },
   ],
   'conditions': [
     [ 'OS=="linux"', {
       'targets': [
         {
           # GN version: //components/exo:wayland
           'target_name': 'exo_wayland',
           'type': 'static_library',
@@ skipping 11 matching lines @@
             'exo/wayland/scoped_wl_types.cc',
             'exo/wayland/scoped_wl_types.h',
             'exo/wayland/server.cc',
             'exo/wayland/server.h',
           ],
         },
       ],
     }],
   ],
 }