Revert of delete the levelDB storage implementation.

components/offline_pages/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")
 }
 
 # GYP: //components/offline_pages.gypi:offline_pages
 static_library("offline_pages") {
   sources = [
     "archive_manager.cc",
     "archive_manager.h",
     "client_policy_controller.cc",
     "client_policy_controller.h",
     "offline_page_archiver.h",
     "offline_page_client_policy.h",
     "offline_page_item.cc",
     "offline_page_item.h",
     "offline_page_metadata_store.cc",
     "offline_page_metadata_store.h",
+    "offline_page_metadata_store_impl.cc",
+    "offline_page_metadata_store_impl.h",
     "offline_page_metadata_store_sql.cc",
     "offline_page_metadata_store_sql.h",
     "offline_page_model.cc",
     "offline_page_model.h",
     "offline_page_storage_manager.cc",
     "offline_page_storage_manager.h",
     "offline_page_types.h",
     "snapshot_controller.cc",
     "snapshot_controller.h",
   ]
 
   deps = [
     ":switches",
     "//base",
     "//components/bookmarks/browser",
     "//components/keyed_service/core",
+    "//components/leveldb_proto",
+    "//components/offline_pages/proto:offline_pages_proto",
     "//net",
     "//sql:sql",
+    "//third_party/leveldatabase",
     "//url",
   ]
 }
 
 static_library("test_support") {
   testonly = true
   sources = [
     "offline_page_test_archiver.cc",
     "offline_page_test_archiver.h",
     "offline_page_test_store.cc",
@@ skipping 31 matching lines @@
     "offline_page_storage_manager_unittest.cc",
     "snapshot_controller_unittest.cc",
   ]
 
   deps = [
     ":offline_pages",
     ":switches",
     ":test_support",
     "//base",
     "//base/test:test_support",
+    "//components/leveldb_proto",
+    "//components/offline_pages/proto:offline_pages_proto",
     "//testing/gtest",
     "//url",
   ]
 }
 
 if (is_android) {
   java_cpp_enum("offline_page_model_enums_java") {
     sources = [
       "offline_page_types.h",
     ]
   }
 }