Record DRP histogram on how long back savings were cleared

components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.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 <stdint.h>
 
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_pref_names.h"
 
 namespace data_reduction_proxy {
 namespace prefs {
@@ skipping 173 matching lines @@
 // before.
 const char kDataReductionProxyWasEnabledBefore[] =
     "spdy_proxy.was_enabled_before";
 
 // An integer pref that contains the time when the data reduction proxy was last
 // enabled. Recorded only if the data reduction proxy was last enabled since
 // this pref was added.
 const char kDataReductionProxyLastEnabledTime[] =
     "data_reduction.last_enabled_time";
 
+// An integer pref that contains the time when the data reduction proxy savings
+// were last cleared because the system clock was moved back by more than 1 day.
+const char kDataReductionProxySavingsClearedNegativeSystemClock[] =
+    "data_reduction.savings_cleared_negative_system_clock";
+
 // An int64_t pref that contains the total size of all HTTP content received
 // from the network.
 const char kHttpReceivedContentLength[] = "http_received_content_length";
 
 // An int64_t pref that contains the total original size of all HTTP content
 // received over the network.
 const char kHttpOriginalContentLength[] = "http_original_content_length";
 
 // An integer pref that contains the Lo-Fi epoch for the implicit opt-out rules.
 // Any time this value is incremented via Finch,
@@ skipping 24 matching lines @@
 
 // Pref to store the retrieval time of the last simulated Data Reduction Proxy
 // configuration. This is part of an experiment to see how many bytes are lost
 // if the Data Reduction Proxy is not used due to configuration being expired
 // or not available.
 const char kSimulatedConfigRetrieveTime[] =
     "data_reduction.simulated_config_retrieve_time";
 
 }  // namespace prefs
 }  // namespace data_reduction_proxy