Add a manifest property declaring USB printers supported by an app.

extensions/extensions_tests.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.
 
 {
   'variables': {
     'extensions_browsertests_sources': [
       'browser/api/audio/audio_apitest.cc',
       'browser/api/bluetooth_socket/bluetooth_socket_apitest.cc',
       'browser/api/dns/dns_apitest.cc',
@@ skipping 83 matching lines @@
       'browser/runtime_data_unittest.cc',
       'browser/sandboxed_unpacker_unittest.cc',
       'browser/value_store/leveldb_value_store_unittest.cc',
       'browser/value_store/testing_value_store_unittest.cc',
       'browser/value_store/value_store_change_unittest.cc',
       'browser/value_store/value_store_frontend_unittest.cc',
       'browser/value_store/value_store_unittest.cc',
       'browser/value_store/value_store_unittest.h',
       'browser/verified_contents_unittest.cc',
       'browser/warning_service_unittest.cc',
+      'common/api/printer_provider/usb_printer_manifest_unittest.cc',
       'common/api/sockets/sockets_manifest_permission_unittest.cc',
       'common/csp_validator_unittest.cc',
       'common/event_filter_unittest.cc',
       'common/extension_l10n_util_unittest.cc',
       'common/extension_resource_unittest.cc',
       'common/extension_set_unittest.cc',
       'common/features/base_feature_provider_unittest.cc',
       'common/features/complex_feature_unittest.cc',
       'common/features/simple_feature_unittest.cc',
       'common/file_util_unittest.cc',
@@ skipping 34 matching lines @@
       'renderer/safe_builtins_unittest.cc',
       'renderer/script_context_set_unittest.cc',
       'renderer/script_context_unittest.cc',
       'renderer/utils_unittest.cc',
       'shell/browser/shell_web_contents_modal_dialog_manager.cc',
       'test/extensions_unittests_main.cc',
       'utility/unpacker_unittest.cc',
     ],
   },
 }