offline_items_collection : Added helper class to determine progress

components/offline_items_collection/core/BUILD.gn

 # Copyright 2017 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/config.gni")
   import("//build/config/android/rules.gni")
 }
 
 static_library("core") {
@@ skipping 80 matching lines @@
       "android/java/src/org/chromium/components/offline_items_collection/bridges/OfflineItemVisualsBridge.java",
     ]
 
     jni_package = "components/offline_items_collection/core/android"
   }
 
   java_cpp_enum("jni_enums") {
     visibility = [ ":*" ]
 
     sources = [
+      "offline_item.h",
       "offline_item_filter.h",
       "offline_item_state.h",
     ]
   }
 }