Reading List iOS: Use external clock in ReadingListEntry.

components/reading_list/ios/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("ios") {
   sources = [
     "favicon_web_state_dispatcher.h",
     "offline_url_utils.cc",
     "offline_url_utils.h",
     "reading_list_entry.cc",
@@ skipping 25 matching lines @@
   public_deps = [
     "//components/reading_list/ios/proto",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "offline_url_utils_unittest.cc",
     "reading_list_entry_unittest.cc",
-    "reading_list_model_unittest.mm",
-    "reading_list_store_unittest.mm",
+    "reading_list_model_unittest.cc",
+    "reading_list_store_unittest.cc",
   ]
   deps = [
     ":ios",
     "//base",
     "//base/test:test_support",
     "//components/sync",
     "//components/sync:test_support_model",
     "//testing/gtest",
     "//url",
   ]
 }