athena: Add the concept of Activity and related managers.

athena/main/athena_main.gyp

 # Copyright 2014 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,
   },
   'targets': [
     {
       'target_name': 'athena_main',
       'type': 'executable',
       'dependencies': [
         '../athena.gyp:athena_lib',
         '../../apps/shell/app_shell.gyp:app_shell_lib',
         '../../skia/skia.gyp:skia',
         '../../ui/accessibility/accessibility.gyp:ax_gen',
         '../../ui/views/views.gyp:views',
       ],
       'include_dirs': [
         '../..',
       ],
       'sources': [
         'athena_launcher.cc',
         'athena_launcher.h',
         'athena_main.cc',
         'placeholder.cc',
         'placeholder.h',
+        'placeholder_content.cc',
+        'placeholder_content.h',
+        'web_activity.cc',
+        'web_activity.h',
       ],
     },
     {
       'target_name': 'athena_shell',
       'type': 'executable',
       'dependencies': [
         '../../base/base.gyp:base',
         '../../base/base.gyp:base_i18n',
         '../../skia/skia.gyp:skia',
         '../../ui/accessibility/accessibility.gyp:ax_gen',
         '../../ui/aura/aura.gyp:aura',
         '../../ui/compositor/compositor.gyp:compositor_test_support',
         '../../ui/gfx/gfx.gyp:gfx',
         '../athena.gyp:athena_lib',
         '../athena.gyp:athena_test_support',
       ],
       'sources': [
         'athena_shell.cc',
+        'sample_activity.cc',
+        'sample_activity.h',
       ],
     }
   ],  # targets
 }