Add the about_page key to shared_module manifest

chrome/chrome_tests_unit.gypi

 # Copyright 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.
 {
   'targets': [
     {
       # This target contains mocks and test utilities that don't belong in
       # production libraries but are used by more than one test executable.
       'target_name': 'test_support_common',
       'type': 'static_library',
@@ skipping 1829 matching lines @@
         'common/extensions/extension_file_util_unittest.cc',
         'common/extensions/extension_icon_set_unittest.cc',
         'common/extensions/extension_unittest.cc',
         'common/extensions/feature_switch_unittest.cc',
         'common/extensions/manifest_handlers/automation_unittest.cc',
         'common/extensions/manifest_handlers/content_scripts_manifest_unittest.cc',
         'common/extensions/manifest_handlers/exclude_matches_manifest_unittest.cc',
         'common/extensions/manifest_handlers/settings_overrides_handler_unittest.cc',
         'common/extensions/manifest_handlers/ui_overrides_handler_unittest.cc',
         'common/extensions/manifest_tests/extension_manifest_test.cc',
+        'common/extensions/manifest_tests/extension_manifests_about_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_background_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_chromepermission_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_contentsecuritypolicy_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_default_extent_path_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_devtools_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_dummy_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_experimental_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_homepage_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_icons_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_initvalue_unittest.cc',
@@ skipping 1005 matching lines @@
             'unit_tests.isolate',
           ],
           'sources': [
             'unit_tests.isolate',
           ],
         },
       ],
     }],
   ],  # 'conditions'
 }