Add a throttle wrapper to OfflineContentProvider

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") {
   sources = [
     "offline_content_aggregator.cc",
     "offline_content_aggregator.h",
     "offline_content_provider.h",
     "offline_item.cc",
     "offline_item.h",
     "offline_item_filter.h",
     "offline_item_state.h",
+    "throttled_offline_content_provider.cc",
+    "throttled_offline_content_provider.h",
   ]
 
   public_deps = [
     "//base",
     "//components/keyed_service/core",
     "//url",
   ]
 
   deps = []
 
   if (is_android) {
     sources += [
       "android/offline_content_aggregator_bridge.cc",
       "android/offline_content_aggregator_bridge.h",
       "android/offline_item_bridge.cc",
       "android/offline_item_bridge.h",
     ]
 
     deps += [ ":jni_headers" ]
   }
 }
 
 source_set("unit_tests") {
   testonly = true
 
   sources = [
     "offline_content_aggregator_unittest.cc",
+    "throttled_offline_content_provider_unittest.cc",
   ]
 
   deps = [
     ":core",
     "//base/test:test_support",
     "//components/offline_items_collection/core/test_support",
   ]
 }
 
 if (is_android) {
@@ skipping 27 matching lines @@
 
   java_cpp_enum("jni_enums") {
     visibility = [ ":*" ]
 
     sources = [
       "offline_item_filter.h",
       "offline_item_state.h",
     ]
   }
 }