Add background-wide file metadata cache.

ui/file_manager/file_manager/background/js/media_scanner_unittest.html

Index: ui/file_manager/file_manager/background/js/media_scanner_unittest.html
diff --git a/ui/file_manager/file_manager/background/js/media_scanner_unittest.html b/ui/file_manager/file_manager/background/js/media_scanner_unittest.html
index 53b60e7302d50ff3003e50a5b1ec26d8b3943fea..529c8bcfb20da96eb2796ef58a9b27a7a886eeab 100644
--- a/ui/file_manager/file_manager/background/js/media_scanner_unittest.html
+++ b/ui/file_manager/file_manager/background/js/media_scanner_unittest.html
@@ -14,10 +14,12 @@
 <script src="../../common/js/volume_manager_common.js"></script>
 <script src="../../common/js/file_type.js"></script>
 <script src="../../common/js/importer_common.js"></script>
+<script src="../../common/js/lru_cache.js"></script>
 <script src="../../common/js/mock_entry.js"></script>
 <script src="../../common/js/mock_file_system.js"></script>
 <script src="../../common/js/unittest_util.js"></script>
 <script src="../../common/js/util.js"></script>
+<script src="metadata_proxy.js"></script>
 <script src="file_operation_util.js"></script>
 <script src="import_history.js"></script>
 <script src="media_scanner.js"></script>