Update data reduction proxy statistics prefs less often on desktop

components/data_reduction_proxy/browser/data_reduction_proxy_prefs.cc

 // 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.
 
 #include "components/data_reduction_proxy/browser/data_reduction_proxy_prefs.h"
 
 #include "base/prefs/pref_registry_simple.h"
 #include "components/data_reduction_proxy/common/data_reduction_proxy_pref_names.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 
@@ skipping 18 matching lines @@
 
 void RegisterSimpleProfilePrefs(PrefRegistrySimple* registry) {
   registry->RegisterBooleanPref(
       data_reduction_proxy::prefs::kDataReductionProxyEnabled, false);
   registry->RegisterBooleanPref(
       data_reduction_proxy::prefs::kDataReductionProxyAltEnabled, false);
   registry->RegisterBooleanPref(
       data_reduction_proxy::prefs::kDataReductionProxyWasEnabledBefore, false);
 }
 
+// Add any new data reduction proxy prefs to the |pref_map_| or the
+// |list_pref_map_| in Init() of DataReductionProxyStatisticsPrefs.
 void RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterInt64Pref(
       prefs::kHttpReceivedContentLength, 0);
   registry->RegisterInt64Pref(
       prefs::kHttpOriginalContentLength, 0);
   registry->RegisterListPref(
       prefs::kDailyHttpOriginalContentLength);
   registry->RegisterListPref(
       prefs::kDailyHttpReceivedContentLength);
   registry->RegisterListPref(
@@ skipping 10 matching lines @@
       prefs::kDailyContentLengthUnknownWithDataReductionProxyEnabled);
   registry->RegisterListPref(
       prefs::kDailyOriginalContentLengthViaDataReductionProxy);
   registry->RegisterListPref(
       prefs::kDailyContentLengthViaDataReductionProxy);
   registry->RegisterInt64Pref(
       prefs::kDailyHttpContentLengthLastUpdateDate, 0L);
 }
 
 }  // namespace data_reduction_proxy