Add test for ReadingListMediator

ios/chrome/browser/ui/reading_list/BUILD.gn

 # Copyright 2016 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.
 
 source_set("reading_list") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "number_badge_view.h",
     "number_badge_view.mm",
     "offline_page_native_content.h",
@@ skipping 65 matching lines @@
   libs = [ "UIKit.framework" ]
 }
 
 source_set("unit_tests") {
   configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "offline_page_native_content_unittest.mm",
     "reading_list_collection_view_controller_unittest.mm",
     "reading_list_coordinator_unittest.mm",
+    "reading_list_mediator_unittest.mm",
   ]
   deps = [
     ":reading_list",
     "//base",
+    "//base/test:test_support",
     "//components/favicon/core",
     "//components/favicon/core/test:test_support",
     "//components/prefs",
     "//components/reading_list/core",
     "//components/url_formatter",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/chrome/browser/favicon",
     "//ios/chrome/browser/reading_list",
     "//ios/chrome/browser/tabs",
     "//ios/chrome/browser/ui",
@@ skipping 58 matching lines @@
     "resources/reading_list_side_swipe@2x.png",
     "resources/reading_list_side_swipe@3x.png",
     "resources/reading_list_toolbar_icon.png",
     "resources/reading_list_toolbar_icon@2x.png",
     "resources/reading_list_toolbar_icon@3x.png",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_file_part}}",
   ]
 }