Update data reduction proxy statistics prefs less often on desktop

components/data_reduction_proxy/browser/BUILD.gn

 # Copyright 2014 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.
 
 static_library("browser") {
   sources = [
     "data_reduction_proxy_auth_request_handler.cc",
     "data_reduction_proxy_auth_request_handler.h",
+    "data_reduction_proxy_delayed_pref_service.cc",
+    "data_reduction_proxy_delayed_pref_service.h"
     "data_reduction_proxy_config_service.cc",
     "data_reduction_proxy_config_service.h",
     "data_reduction_proxy_configurator.h",
     "data_reduction_proxy_metrics.cc",
     "data_reduction_proxy_metrics.h",
     "data_reduction_proxy_params.cc",
     "data_reduction_proxy_params.h",
     "data_reduction_proxy_prefs.cc",
     "data_reduction_proxy_prefs.h",
     "data_reduction_proxy_protocol.cc",
@@ skipping 28 matching lines @@
     "//net",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }
 
 source_set("unit_tests") {
   sources = [
     "data_reduction_proxy_auth_request_handler_unittest.cc",
+    "data_reduction_proxy_delayed_pref_service_unittest.cc",
     "data_reduction_proxy_config_service_unittest.cc",
     "data_reduction_proxy_metrics_unittest.cc",
     "data_reduction_proxy_params_unittest.cc",
     "data_reduction_proxy_protocol_unittest.cc",
     "data_reduction_proxy_settings_unittest.cc",
     "data_reduction_proxy_usage_stats_unittest.cc",
   ]
 
   deps = [
     ":browser",
     ":test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }