[Offline Pages] Add cached offline page utils and show usage in settings.

components/offline_pages/core/BUILD.gn

 # 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.
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 static_library("core") {
   sources = [
     "archive_manager.cc",
     "archive_manager.h",
+    "cached_offline_page_utils.cc",
+    "cached_offline_page_utils.h",
     "client_namespace_constants.cc",
     "client_namespace_constants.h",
     "client_policy_controller.cc",
     "client_policy_controller.h",
     "offline_event_logger.cc",
     "offline_event_logger.h",
     "offline_page_archiver.h",
     "offline_page_client_policy.h",
     "offline_page_item.cc",
     "offline_page_item.h",
@@ skipping 62 matching lines @@
   deps = [
     "//base",
     "//components/version_info",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "archive_manager_unittest.cc",
+    "cached_offline_page_utils_unittest.cc",
     "client_policy_controller_unittest.cc",
     "offline_event_logger_unittest.cc",
     "offline_page_metadata_store_unittest.cc",
     "offline_page_model_event_logger_unittest.cc",
     "offline_page_model_impl_unittest.cc",
     "offline_page_model_query_unittest.cc",
     "offline_page_storage_manager_unittest.cc",
     "snapshot_controller_unittest.cc",
     "task_queue_unittest.cc",
     "task_unittest.cc",
@@ skipping 18 matching lines @@
     sources = [
       "background/request_notifier.h",
       "background/request_queue_results.h",
       "background/save_page_request.h",
       "downloads/download_ui_item.h",
       "offline_page_types.h",
       "offline_store_types.h",
     ]
   }
 }