Record DRP histogram on how long back savings were cleared

components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats_unittest.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/core/browser/data_reduction_proxy_compression_stats.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <string>
@@ skipping 981 matching lines @@
       FakeNow());
   int64_t original2[] = {kOriginalLength * 2, kOriginalLength};
   int64_t received2[] = {kReceivedLength * 2, kReceivedLength};
   VerifyDailyDataSavingContentLengthPrefLists(
       original2, 2, received2, 2,
       original2, 2, received2, 2,
       original2, 2, received2, 2);
 }
 
 TEST_F(DataReductionProxyCompressionStatsTest, BackwardTwoDays) {
+  base::HistogramTester histogram_tester;
   const int64_t kOriginalLength = 200;
   const int64_t kReceivedLength = 100;
   int64_t original[] = {kOriginalLength};
   int64_t received[] = {kReceivedLength};
 
   RecordContentLengthPrefs(
       kReceivedLength, kOriginalLength, true, VIA_DATA_REDUCTION_PROXY,
       FakeNow());
   // Backward two days.
   SetFakeTimeDeltaInHours(-2 * 24);
   RecordContentLengthPrefs(
       kReceivedLength, kOriginalLength, true, VIA_DATA_REDUCTION_PROXY,
       FakeNow());
   VerifyDailyDataSavingContentLengthPrefLists(
       original, 1, received, 1,
       original, 1, received, 1,
       original, 1, received, 1);
+  histogram_tester.ExpectUniqueSample(
+      "DataReductionProxy.CountSavingsCleared.NegativeSystemClock", 1, 1);
+  VerifyPrefInt64(prefs::kDataReductionProxySavingsClearedNegativeSystemClock,
+                  FakeNow().ToInternalValue());
 }
 
 TEST_F(DataReductionProxyCompressionStatsTest, NormalizeHostname) {
   EXPECT_EQ("www.foo.com", NormalizeHostname("http://www.foo.com"));
   EXPECT_EQ("foo.com", NormalizeHostname("https://foo.com"));
   EXPECT_EQ("bar.co.uk", NormalizeHostname("http://bar.co.uk"));
   EXPECT_EQ("http.www.co.in", NormalizeHostname("http://http.www.co.in"));
 }
 
 TEST_F(DataReductionProxyCompressionStatsTest, RecordUma) {
@@ skipping 281 matching lines @@
   expected_data_usage =
       base::MakeUnique<std::vector<data_reduction_proxy::DataUsageBucket>>(
           kNumExpectedBuckets);
   DataUsageLoadVerifier verifier2(std::move(expected_data_usage));
   LoadHistoricalDataUsage(base::Bind(&DataUsageLoadVerifier::OnLoadDataUsage,
                                      base::Unretained(&verifier2)));
   base::RunLoop().RunUntilIdle();
 }
 
 }  // namespace data_reduction_proxy