Adding a DataSavingsRecorder interface

components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats_unittest.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats_unittest.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats_unittest.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats_unittest.cc
index 071dc4ff90eb5facb1f158bad585a37e292c8289..4c97d2f6c3dfa03f7886a6fb5a5ba1108a976a87 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats_unittest.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_compression_stats_unittest.cc
@@ -595,20 +595,42 @@ TEST_F(DataReductionProxyCompressionStatsTest, TotalLengths) {
       kReceivedLength, kOriginalLength, IsDataReductionProxyEnabled(),
       UNKNOWN_TYPE, nullptr, std::string());
 
   EXPECT_EQ(kReceivedLength * 2,
             GetInt64(data_reduction_proxy::prefs::kHttpReceivedContentLength));
   EXPECT_FALSE(IsDataReductionProxyEnabled());
   EXPECT_EQ(kOriginalLength * 2,
             GetInt64(data_reduction_proxy::prefs::kHttpOriginalContentLength));
 }
 
+TEST_F(DataReductionProxyCompressionStatsTest, TotalLengthsUpdate) {
+  const int64_t kOriginalLength = 200;
+  const int64_t kReceivedLength = 100;
+
+  compression_stats()->UpdateDataSavings(std::string(), kReceivedLength,
+                                         kOriginalLength);
+
+  EXPECT_EQ(0,
+            GetInt64(data_reduction_proxy::prefs::kHttpReceivedContentLength));
+  EXPECT_EQ(kOriginalLength - kReceivedLength,
+            GetInt64(data_reduction_proxy::prefs::kHttpOriginalContentLength));
+
+  // Record the same numbers again, and total lengths should be doubled.
+  compression_stats()->UpdateDataSavings(std::string(), kReceivedLength,
+                                         kOriginalLength);
+
+  EXPECT_EQ(0,
+            GetInt64(data_reduction_proxy::prefs::kHttpReceivedContentLength));
+  EXPECT_EQ(kOriginalLength * 2 - kReceivedLength * 2,
+            GetInt64(data_reduction_proxy::prefs::kHttpOriginalContentLength));
+}
+
 TEST_F(DataReductionProxyCompressionStatsTest, OneResponse) {
   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());