Record DRP histogram on how long back savings were cleared

components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.cc
index ee018ffec3b98214ba8e3fd2d32907792bb7fbe9..4e6cb863dbe8b40a2ddad472bddf17b83f37dffa 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.cc
@@ -277,6 +277,22 @@ void DataReductionProxySettings::MaybeActivateDataReductionProxy(
           (clock_->Now() - base::Time::FromInternalValue(last_enabled_time))
               .InDays());
     }
+
+    int64_t last_savings_cleared_time = prefs->GetInt64(
+        prefs::kDataReductionProxySavingsClearedNegativeSystemClock);
+    if (last_savings_cleared_time != 0) {
+      int32_t days_since_savings_cleared =
+          (clock_->Now() -
+           base::Time::FromInternalValue(last_savings_cleared_time))
+              .InDays();
+
+      // Sample in the UMA histograms must be at least 1.
+      if (days_since_savings_cleared == 0)
+        days_since_savings_cleared = 1;
+      UMA_HISTOGRAM_CUSTOM_COUNTS(
+          "DataReductionProxy.DaysSinceSavingsCleared.NegativeSystemClock",
+          days_since_savings_cleared, 1, 365, 50);
+    }
   }
 
   if (spdy_proxy_auth_enabled_.GetValue() &&