Allow manifest handlers to declare keys they depend on that must be parsed before them.

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 1503 matching lines @@
         'common/extensions/manifest_tests/extension_manifests_validapp_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_web_accessible_resources_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_web_intents_unittest.cc',
         'common/extensions/manifest_tests/extension_manifests_web_unittest.cc',
         'common/extensions/matcher/regex_set_matcher_unittest.cc',
         'common/extensions/matcher/string_pattern_unittest.cc',
         'common/extensions/matcher/substring_set_matcher_unittest.cc',
         'common/extensions/matcher/url_matcher_unittest.cc',
         'common/extensions/matcher/url_matcher_factory_unittest.cc',
         'common/extensions/manifest_unittest.cc',
+        'common/extensions/manifest_handler_unittest.cc',
         'common/extensions/message_bundle_unittest.cc',
         'common/extensions/permissions/api_permission_set_unittest.cc',
         'common/extensions/permissions/permission_set_unittest.cc',
         'common/extensions/permissions/media_galleries_permission_unittest.cc',
         'common/extensions/permissions/socket_permission_unittest.cc',
         'common/extensions/unpacker_unittest.cc',
         'common/extensions/update_manifest_unittest.cc',
         'common/extensions/user_script_unittest.cc',
         'common/extensions/value_counter_unittest.cc',
         'common/extensions/api/extension_api_unittest.cc',
@@ skipping 835 matching lines @@
               # more details.
               'DebugInformationFormat': '3',
               'ProgramDataBaseFileName': '<(PRODUCT_DIR)/unit_tests.exe.pdb',
             },
           },
         },
       ],
     }],
   ],  # 'conditions'
 }