Update data reduction proxy statistics prefs less often on desktop

components/data_reduction_proxy/browser/data_reduction_proxy_metrics.cc

Index: components/data_reduction_proxy/browser/data_reduction_proxy_metrics.cc
diff --git a/components/data_reduction_proxy/browser/data_reduction_proxy_metrics.cc b/components/data_reduction_proxy/browser/data_reduction_proxy_metrics.cc
index 2093d841ad81082b308dd79055433b449c75aa38..780284b60889c559654278a28241da360b5f0b17 100644
--- a/components/data_reduction_proxy/browser/data_reduction_proxy_metrics.cc
+++ b/components/data_reduction_proxy/browser/data_reduction_proxy_metrics.cc
@@ -5,10 +5,9 @@
 #include "components/data_reduction_proxy/browser/data_reduction_proxy_metrics.h"
 
 #include "base/metrics/histogram.h"
-#include "base/prefs/pref_service.h"
-#include "base/prefs/scoped_user_pref_update.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
+#include "components/data_reduction_proxy/browser/data_reduction_proxy_delayed_pref_service.h"
 #include "components/data_reduction_proxy/browser/data_reduction_proxy_settings.h"
 #include "components/data_reduction_proxy/common/data_reduction_proxy_headers.h"
 #include "components/data_reduction_proxy/common/data_reduction_proxy_pref_names.h"
@@ -194,14 +193,14 @@ class DailyContentLengthUpdate {
  public:
   DailyContentLengthUpdate(
       const char* pref,
-      PrefService* pref_service)
-      : update_(pref_service, pref) {
+      DataReductionProxyDelayedPrefService* pref_service)
+      : update_(pref_service->GetList(pref)) {
   }
 
   void UpdateForDataChange(int days_since_last_update) {
     // New empty lists may have been created. Maintain the invariant that
     // there should be exactly |kNumDaysInHistory| days in the histories.
-    MaintainContentLengthPrefsWindow(update_.Get(), kNumDaysInHistory);
+    MaintainContentLengthPrefsWindow(update_, kNumDaysInHistory);
     if (days_since_last_update) {
       MaintainContentLengthPrefForDateChange(days_since_last_update);
     }
@@ -209,7 +208,7 @@ class DailyContentLengthUpdate {
 
   // Update the lengths for the current day.
   void Add(int content_length) {
-    AddInt64ToListPref(kNumDaysInHistory - 1, content_length, update_.Get());
+    AddInt64ToListPref(kNumDaysInHistory - 1, content_length, update_);
   }
 
   int64 GetListPrefValue(size_t index) {
@@ -248,10 +247,10 @@ class DailyContentLengthUpdate {
 
     // Entries for new days may have been appended. Maintain the invariant that
     // there should be exactly |kNumDaysInHistory| days in the histories.
-    MaintainContentLengthPrefsWindow(update_.Get(), kNumDaysInHistory);
+    MaintainContentLengthPrefsWindow(update_, kNumDaysInHistory);
   }
 
-  ListPrefUpdate update_;
+  base::ListValue* update_;
 };
 
 // DailyDataSavingUpdate maintains a pair of data saving prefs, original_update_
@@ -264,7 +263,7 @@ class DailyDataSavingUpdate {
   DailyDataSavingUpdate(
       const char* pref_original,
       const char* pref_received,
-      PrefService* pref_service)
+      DataReductionProxyDelayedPrefService* pref_service)
       : original_(pref_original, pref_service),
         received_(pref_received, pref_service) {
   }
@@ -339,7 +338,8 @@ void UpdateContentLengthPrefsForDataReductionProxy(
     int original_content_length,
     bool with_data_reduction_proxy_enabled,
     DataReductionProxyRequestType request_type,
-    base::Time now, PrefService* prefs) {
+    base::Time now,
+    DataReductionProxyDelayedPrefService* prefs) {
   // TODO(bengr): Remove this check once the underlying cause of
   // http://crbug.com/287821 is fixed. For now, only continue if the current
   // year is reported as being between 1972 and 2970.
@@ -478,7 +478,7 @@ void UpdateContentLengthPrefs(
     int original_content_length,
     bool with_data_reduction_proxy_enabled,
     DataReductionProxyRequestType request_type,
-    PrefService* prefs) {
+    DataReductionProxyDelayedPrefService* prefs) {
   int64 total_received = prefs->GetInt64(
       data_reduction_proxy::prefs::kHttpReceivedContentLength);
   int64 total_original = prefs->GetInt64(